Sanity Slippage



""Because madness, as you know, is like gravity. All it takes is a little push!" (Laughs maniacally)"

- The Joker, The Dark Knight Saga

A character has been a bit ... off for a while now. Maybe they just haven't been themselves, maybe they've gone as far as painting a Room Full of Crazy while reciting a Madness Mantra, or maybe they've gone through a Madness Makeover, but it's apparent from their actions that their rational mind is losing its grip and they are sliding inch by inch toward insanity.

The end result of this varies, depending on the tone of the series and who the character is. If the series is dark and edgy, they may go on a murderous rampage. On the other hand, if it's light and soft, it may just be Played for Laughs, becoming a source for their hilarious dialogue and wacky plans. A villain is likely to have a Villainous Breakdown resulting in Karmic Death, while a hero will just have a Heroic BSOD and then get better.

Occasionally, a character will be seen holding back their insanity and generally keeping in check, until that final straw breaks the camel's back and they finally snap, having a massive Freak-Out.

And most rarely, the Sanity Slippage is the effect of an Insanity Ploy on a victim by the Villain.

A Super-Trope to Sanity Slippage Song.

Compare Freak-Out, Villainous Breakdown, Room Full of Crazy, Madness Mantra, Laughing Mad, and With Great Power Comes Great Insanity.

Anime and Manga
"Newscaster: Lets all love Lain! Lets all love Lain! Lets all love Lain LainLainLain!!!"
 * Higurashi no Naku Koro ni has this occur several times, often bloodily.
 * Heck, pretty much once an arc. are really freaking scary when they completely lose it.
 * The sister series, Umineko no Naku Koro ni, reveals in the fifth arc that has slowly been losing it since  two years before the story begins.
 * Arc 3 of Umineko also has really losing it, first after  and then after  By the end of the arc, she's gone completely apeshit and.
 * By the end of Serial Experiments Lain, most of the characters, major and minor, including to some extent, Lain herself.
 * Hell, it's implied to happen all over the world.


 * Happens quite a few times in Code Geass, with results ranging from a Heroic BSOD to Insane Laugh.
 * One particularly notable incident from Code Geass is when
 * Tengen Toppa Gurren Lagann has Simon going Ax Crazy while fighting enemy mechas, locking himself on his room almost 24/7, and spending all his time carving statues out of stone. Luckily, he finally does a 180° flip.
 * Makoto in RahXephon teeters on the edge until his grand scheme bites him in the ass, at which point he takes the thrilling plunge into insanity.
 * An entire episode of Elfen Lied is dedicated to the Ax Crazy protagonist Lucy's childhood, in which we get to see just how she got so unstable and murderous through this trope.
 * In Fullmetal Alchemist, Scar's older brother is revealed to have suffered this. The combination of his lover's death, failing to revive her through human transmutation, and the imposing threat of a war on his home eventually pushed him over the edge. Using his own body, he planned to create a Philosopher's Stone out of Ishbal's people during the massacre. He wandered out onto the battlefield completely naked with Ax Crazy eyes and tears streaming down his face as Scar watched in horror. It didn't end well.
 * First anime only, please note. In the manga and Brotherhood, this self-taught alchemist, name unknown, is the only person apart from the immortal Van Hohenheim (who knew the villain personally) to work out what is wrong with Amestris and its alchemy, why the Ishbal War was started, what is going to happen on the Promised Day, and how to stop it.
 * He then dies heroically saving his little brother's life, leaving his essential research in his care. All the more you could ask is that he'd been slightly better at communicating, so his brother had the faintest idea what he was carrying and what the Amestrians were really working toward.
 * This happens to Shou Tucker as well in the first anime - his madness is depicted as being far more explicit and (somehow) more forgivable than in the manga. Here, instead of meeting his Karmic Death at the hands of Scar, he continues to live aiding the homunculi and experimenting on his own body (turning him into hideous monster) in hopes of bringing back the daughter he sacrificed, with the help of the Philosopher's Stone. Upon realizing that he only got an Empty Shell, Tucker completely breaks down into a gibbering wreck, trying to relive the happy memories he had with his daughter before she became a victim of his research.
 * Fairly late in the manga (chapter 82), after the second Greed kills the first Greed's old minion Bido, while the poor chimera insisted they were friends, he goes through some very rapid sanity slippage, due to triggering memories he believed shouldn't exist. Greed gets very attached to people who are his, but he was also pretty insistent that he was a different person than the previous Greed. Ling in his head shouting about the indissoluble bonds of the soul did not help with the screaming-flashback identity crisis problem.
 * Once he pulls himself mostly together again he adopts the only slightly saner behavior of attacking his brother Wrath, shouting through the whole epic fight about how Wrath killed all his 'possessions.' Then he goes off and pulls a Heel Face Turn as Ed's 'boss'-slash-Token Evil Teammate, with a series of excuses about how it's for his own benefit that last right about till
 * Bleach:
 * Ichigo Kurosaki exhibited some Sanity Slippage
 * In Romeo X Juliet, after witnessing, quickly starts losing it.
 * Soul Eater:
 * Professor Stein goes completely insane as a result of Medusa's plans., but still the entire collection of scenes showing his descent into madness is creepy.
 * Sort of applies to Soul Eater as well,
 * The entire cast is constantly teetering on the edge of this trope. Madness functions as The Dark Side in the Soul Eater universe, with characters falling into madness becoming evil and others resisting the temptation to madness. One of the major villains is someone who slipped so far into insanity that he became an Eldritch Abomination.
 * The manga-verse now holds that he's apparently insane because he's an Eldritch Abomination personifying a kind of madness. Same point reveals that is the next in line for slipping.
 * In Gankutsuou, we get this when At first he sobs desperately and then he breaks out into hysterical laughter. And from then on, he's out there, madly pursuing his revenge.  also does this, going from creepy to outright deranged by the end of the series. And let's not forget, preceded by a good amount of madness...oh, and . Or Héloise de Villefort. Yeah, this show is pretty much filled with the trope.
 * Gyagu Manga Biyori has the tale of the son and father who wanted to hire a tutor (and chose her more for the sake of her looks than the help she would give), but take many days to realize that they were tricked (Of course, like everything else, it is done in such a way that you have to laugh). At first they just look depressed when she doesn't show up, then their hands start bleeding because they clench their fists so hard and are beating the walls... their explanation for her absence is that they don't have a welcoming enough feeling in their home. Cut to them dressed as clowns as the father keeps stabbing a rock-hard cake while shouting "She won't come!" several times, mixed with laughter... It becomes an Inverted Trope when they then grab a hold of themselves and they work their way to becoming pure levitating buddhists.
 * Naruto:
 * Itachi displayed this during his fight against, while claiming that , and suggests this is his true self.
 * Sasuke plays it straight, though. As if deciding to murder everyone in the Leaf Village weren't enough, he outright hits the floor in chapter 480 and the few after it. He's basically been reduced to a homicidal maniac who will kill anyone if they become the least bit inconvenient to him.
 * Orochimaru went through this in his backstory, but managed to conceal it enough that he'd already been kidnapping people for depraved experiments for ages when Sarutobi finally worked it out. Nagato went through something more like a Heroic BSOD that resulted in a Madness Makeover to Pain, but there was enough of a time spread that he definitely had time to devolve gradually. As Madness Makeovers go, wearing your murdered friend's corpse as a puppet avatar is pretty near the top.
 * Gaara qualifies for this from his flashbacks. As a kid he was initially sweet and misunderstood. Then his father started sending people he loved to assassinate him. Fast forward to his early teens, and he's a homicidal maniac talking to sand as though it's his dead mother. Luckily he recovered.
 * Kabuto lost quite a bit of sanity after.
 * from The Twelve Kingdoms falls into this due to him getting closer and closer to the Despair Event Horizon as he's Trapped in Another World.
 * Neon Genesis Evangelion has a cast that display their loss of sanity in different ways... some a little more disturbing than others.
 * End of Evangelion decides to do away with the incremental slips and jumps right off the edge thanks to the ritual to awaken Lilith leaving Shinji a shrieking broken mess.
 * Kaede from SHUFFLE!. In the anime version, anyway.
 * Sekai and especially Kotonoha in School Days.
 * Ookamikakushi: Issei in the few episodes he appears in until he.
 * Light Yagami from Death Note, possibly.
 * Given he gets an iconic evil Laughing Mad scene, Light Yagami almost certainly. Unless you feel he represents a viable alternate moral structure, with oneself as the measure of all things.
 * Dilandau Albatou from Vision of Escaflowne is a subverted example. He was already kind of Ax Crazy to begin with, but after Van, Dilandau's already fragile state of mind went downhill from there.
 * In Stepping on Roses (Hadashi de Bara wo Fume),
 * In episode 7 of Puella Magi Madoka Magica, we can see breaking down fast as she fights a witch. Why?  That was just the last straw, though. Other factors certainly helped.
 * In Gregory Horror Show, the Hell Hotel can only be found by people who have already begun to slip a little (the first guest and the second guest ). Prolonged exposure to it breaks the guests more and more.
 * Weiss Kreuz:
 * Youji Kudou begins slowly losing his mind after killing his would-be love interest before she could kill him first (although close scrutiny will reveal a few hints of it beforehand, such as a manga scene where he mistakes Omi for her after waking up from a nightmare). Before it's over, he's nearly killed several one-night stands and had several long conversations with the woman's ghost.
 * Ken Hidaka doesn't fare much better: starting with the two-part OVA Verbrechen ~ Strafe, he finds himself enjoying the act of killing more and more, goaded along by having to fake killing his teammates and having to actually kill his girlfriend when she turns into a target. He manages to avoid falling so far as to start killing people on his own time, but in the Radio Drama Fight Fire With Fire, set after Weiss has been dissolved, he tries to convince Aya to become the new Persia so that he'll have someone to tell him who he can kill.
 * Gintama: Yamazaki has one in an episode where he's running a stake out and can only eat anpan and milk. Watch it here.
 * Quite a few characters in Pandora Hearts go through this at one point or another, like Leo after  or Oz when he goes into Love Makes You Crazy mode for Alice. (He gets slapped out of it by Gil).
 * Mirai Nikki: Yukiteru. Yuno doesn't count because that would imply that she was sane to begin with.
 * Mima and Rumi of Perfect Blue both experience this. Mima gets better but Rumi doesn't.
 * Koharu Mutsuki Koharu no Hibi acts more Yandere as the story progresses as a result of her love for Akira.
 * In Saint Beast, Zeus becomes increasingly insane as the series progresses.
 * Relatively rare in Trigun, all things considered—most of the insane people are already insane when introduced, including, in two cases, during the kid part of their Used to Be a Sweet Kid reveal. The only serious case of Sanity Slippage in the manga is actually Vash.
 * A bit in-continuity, but mostly during the SEEDs flashback, after Rem gets Vash and Knives out of the medbay where they learned the awful truth and promptly attempted to starve to death. Vash persists in wanting to die and hating humans, stabs Rem in the side in the course of a fight over a fruit knife he hopes to use on himself, and for a really awful moment, he smiles. Then he breaks down crying, patches her up, and things start to be okay again.
 * Notably, Knives didn't get this. Knives went promptly and utterly over to mad from the revelation, and acted like he'd blocked it out and was perfectly okay right up until enacting Plan Kill All Humans.
 * Legato also devolves steadily and horribly over the course of Maximum—yes, he was already bonkers, but after Knives breaks his spine he falls apart rapidly. Though he doesn't get less dangerous—after all People Puppets are his specialty.
 * You could make cases for other characters—Knives' A Nazi by Any Other Name Nietzsche Wannabe material slides up into A God Am I territory and so on. But none of them start sane.

Comic Books

 * The Killing Joke is one take on the Sanity Slippage that eventually led to the origin of The Joker. But the Joker admits he's an Unreliable Narrator and could be remembering wrong or making the whole thing up. He attempts something similar to crack
 * Rorschach from Watchmen is clearly mentally unstable even before the event that causes him to slide off of the slippery slope.
 * Jackson Georges from Ex Machina, Mayor Hundred's former NSA handler fits this trope. In flashbacks the reader is shown how the cryptic shard that Mitchell found when he got his powers slowly drives Jackson to levels of extreme paranoia. He develops an unfounded contempt for Mitchell, claiming that without Mitchell's appearance and the mystery of the shard, he could have foreseen and prevented 9/11. He becomes obsessed with protecting his family from dirty bombs and the like, buying a Hazmat Suit and making tally marks on the wall to represent god knows what. It's clear he's a step away from the deep end. Darkly subverted when

Fan Works

 * Jack O'Lantern, the Arch Enemy of Spider-Woman, commits increasingly violent and destructive crimes as the series progresses. He goes from robbing banks to taking people hostage to going on killing sprees to orchestrating a bloody city-wide Mob War. Even in jail, we see him fantasizing about carving up human heads the way people do Halloween pumpkins. What's unusual is that Jack always had these sadistic urges-the Sanity Slippage comes from the escalating nature of his crimes.
 * Austria/Roderich Edelstein in the 1983 Doomsday Stories is portrayed for the most part as undergoing through this. His obsession in finding out whether Hungary survived Doomsday grows increasingly desperate (and irrepressible) over time to the point that others eventually start wondering if he's gone delusional from grief. It's also mentioned to have happened as well with Romano (hijacked by The Mafia as his brother's successor) and Poland (having his personality shattered).

Film

 * Francesco Dellamorte-Dellamore in Cemetery Man - this is, in fact, the whole plot of the film.
 * Zac Hobson in The Quiet Earth begins suffering this when he realises that he may very well be the last human being alive. After the Good Times Montage, he begins dressing in women's clothes; he fills his garden with cardboard cutouts of celebrities; he fires his shotgun wildly at televisions; he declares himself President of the World and gives his inaugural address to the cutouts. And then the power goes out, leaving Zac standing on his balcony, in total darkness and utterly insane. He gets better.
 * Eric in Killing Zoe wasn't exactly the sanest person to begin with, but doing copious amounts of heroin, murdering several people, and setting off some explosives cause him to become batshit insane. As further proof, one of his favorite threats towards the end are "I'll fuck your bitch up the ass and give her AIDS!"
 * Stéphane in The Science of Sleep always had rather odd and confusing dreams and Image Spots to help his cope with reality... by the end of the film he's unable to tell the difference between the two. While it doesn't go all the way to the end he holds shades of this.
 * Happens to Komodo in Warriors of Virtue after he . Although he was pretty zany from the start, he seemed to drop a few notches after the event.
 * Although Trevor Reznik from The Machinist had been acting odd ever since, when he starts harassing and assaulting everyone around him in a paranoid conviction that they are all out to get him you can tell he has finally completely cracked.
 * Mike in Deep End suffers this, mostly courtesy of Susan. The entire plot of the movie is Mike becoming her Stalker with a Crush—except it's rather hard to understand why, considering her personality—and in the end Given how she treated him throughout the entire movie, it's hard to sympathize with her.
 * in Session 9, although whether it's insanity or some sort of supernatural possession is left deliberately ambiguous.
 * The main character in I Am Legend suffers the beginnings of sanity slippage, asking a mannequin to talk to him because he promised his dog he'd ask, then breaking down in tears because the mannequin does not answer. It's even worse in the deleted scenes/uncut version. When he drives past the mannequin  the head of the mannequin actually moves, and when he wakes up , he first sees the people in his house as his own wife and daughter
 * This trope is the whole point of Black Narcissus. All of the nuns find their flaws and emotional weaknesses slowly becoming more and more exaggerated. Things are worst with Sister Ruth, none too well to begin with, who turns into a Stalker with a Crush, and winds up
 * In the classic The Treasure of the Sierra Madre, Dobbs becomes increasingly unhinged as greed and paranoia brought on by Gold Fever sets in, eventually leading him to try to murder everyone in his group.
 * Ursula of The Little Mermaid. While not a good character, she was sane and composed during most of the film. However, when she transforms into Vanessa, its implied that she lost quite a bit of sanity (to the point of becoming a borderline Ax Crazy) when turning into her, as she talks to her mirror in a manner similar to a schizophrenic, emits a psychotic grin when throwing a pin at a mirror's head with enough velocity to knock the mirror back, and most certainly kill a person had that been a human being, not to mention her cackling.
 * Harvey Dent in The Dark Knight Saga screaming in silent agony in the hospital after realizing that . From there his Sanity Slippage is evident, especially following The Joker's disturbing Hannibal Lecture on him.
 * Alex Forrest in Fatal Attraction grows increasingly unhinged the more Dan Gallagher tries to distance himself from her, until she reaches the point where she's willing to boil his daughter's bunny in the pressure cooker, kidnap her, and then try to knife his wife to death.
 * Jafar in Aladdin.
 * In The Assassination of Richard Nixon Samuel Byck (who was a real person) experiences this. Initially he just seems like a slightly delusional loser, but eventually he
 * In Cross of Iron Steiner goes through this as he's recovering in hospital. Even more so
 * The documentary Touching The Void is about the two climbers Joe Simpson and Simon Yates in their attempt to climb the Siula Grande mountain. After Joe Simpson has had his rope cut and been days without barely any food or water, he eventually becomes delirious. We are also shown how as he presumes himself to be close to death the song 'Brown Girl in the Ring' by Boney M get's stuck in his head, which is a song that he hates.

Literature

 * Johnny Truant and Zampano in House of Leaves.
 * Gollum and Denethor in The Lord of the Rings.
 * Isildur after he gets the Ring.
 * Jack Torrance in The Shining. Stephen King stated his book was about a normal man who goes crazy, and that Stanley Kubrick's film was about a crazy man who goes absolutely bonkers.
 * Roland goes through this in the first third or so of The Dark Tower due to
 * Rand Al'Thor of The Wheel of Time certainly seems to inhabit this trope over the course of at least seven Doorstoppers. More pressures, more sacrifices and mistakes, more obvious signs of mental instability. After he is he snaps completely. He adopts Dissonant Serenity and engages in more and more questionable deeds. After  he seems to be showing signs of addressing the slippage though.
 * The narrator from The Moth Diaries. Possibly.
 * Everyone in The Republic Of Trees:
 * Alex:
 * Isobel:
 * Louis:
 * Joy:
 * Michael, the most notable, being the narrator: over a couple of chapters  By the end of the story he is so broken, that when he discovers what , he decides to just roll with it.
 * The narrator of The Yellow Wallpaper. Understandable, when you're locked in the attic for months, almost totally deprived of outside interaction.
 * Very common in H.P. Lovecraft's work, most notably in "The Rats in the Walls" and "A Shadow Over Innsmouth." Of course, considering the type of stories he wrote, it's understandable.
 * Warrior Cats:, and to a lesser extent, her brothers.
 * Most Redwall books have at least one villainous character go through this.
 * Alicia DeVries of In Fury Born suffers this throughout the second half of the book due to being possessed by the last of the Greek Furies. Culminates when she discovers the identities of the traitors within, and subsequently goes batshit crazy. Fortunately, she is stopped   by the Fury and her ship's AI in a Battle in the Center of the Mind.
 * Dr. Seward in his appearance in Anno Dracula. You have to give him a little insanity though; it's an Alternate History of Dracula where instead of the Earn Your Happy Ending situation of rescuing Britain from a supernatural evil while losing (only) your fiancee and an American friend, he lives through a Diabolus Ex Machina Kill 'Em Or Corrupt 'Em scenario. If he still had his sanity, he'd be closer to an Idiot Hero by this point.
 * In the original Dracula Jonathan Harker and Renfield experienced this thanks to the Count. Harker recovered, Renfield, not so much.
 * In Diary of a Madman, the eponymous diary details the descent of Poprishchin descent into madness, starting with his delusion that he can understand dogs and their letters.
 * Alfred Lambert in The Corrections.
 * Happens to a few characters in The Pale King, most notably David Cusk and.
 * In Max Barry's Machine Man, the main character, Dr. Charles Neumann, suffers from this. While not quite 'normal' to begin with, after.
 * Jaimy in the Bloody Jack series. Early in My Bonny Light Horseman, he receives a head wound in battle that doesn't get treated for weeks because he's in a French prison. As the series progresses, you can see him slowly spiraling down to his Heroic BSOD in The Mark Of The Golden Dragon.
 * In Therese Raquin, the more time passes, the more Thérèse and Laurent are haunted by memories of Camille, and the crazier they become.
 * Lydia in Caught In The Act.
 * A Song of Ice and Fire: While had never been completely grounded, she wasn't completely off her rocker either. Over the course of the fourth book, though, in response to , she starts losing it, seeing enemies in every corner and ordering people tortured willy-nilly.

Live Action TV

 * Dexter wrestles with Sanity Slippage during the second season of the series.
 * Half the fun of Farscape.
 * One of the tie-in bits of promotional material for the Firefly movie Serenity is a short series of films called the "R. Tam Sessions," which depict River's traumatic time at the Academy. It starts off with River being a happy, eager girl who really wants to learn and push herself to her limits, but as the series progresses, she is shown slipping into madness due to the Academy's experiments. The series ends with River killing the man who has been interviewing her by shoving a pen through his throat (who, for those of you playing at home, was played by Joss Whedon).
 * During Volume 4 of Heroes, Sylar's already-unstable psyche takes a dramatic turn for the worse when he acquires the ability to shapeshift and starts to lose his sense of identity after using it repeatedly.
 * Although it's never shown, during Mash's finale, after witnessing a traumatic event, Hawkeye begins to not-so-subtly show signs of a breakdown. Like being convinced one of the anesthesiologists was attempting to suffocate his patient with the gas mask, or crashing a jeep through the mess tent. . Little indications of a stressful work environment.
 * Simon Bellamy from the British sci-fi series Misfits is a painfully shy and intense introvert (and convicted arsonist) who has been bullied and ignored all his life; it's hinted from the onset that he's teetering on the verge of mental breakdown. As the series continues he accidentally becomes party to murder, is magically imbued with the power of Invisibility (which, awesome as it sounds, greatly heightens his growing sense of alienation and his unhealthy tendencies towards voyeurism) and During the final episode of Season 1, the full extent of his sanity slippage is magnificently depicted as he  He got better though.
 * Series one also shows Sally the probation worker go through a (arguably milder) version of this. Tony, the previous probation worker was her fiance and she spends the whole season trying to prove that the gang is behind his mysterious disappearance. (and she's right about it), though she spends most her time stalking the misfits and by the end became completely obsessed by this.
 * The Master from Doctor Who has always been rather unstable, try as he might to hide it under his veneer of a Magnificent Bastard. However, this takes a turn for the worse in NuWho, when he complains of a persistent drumming in his head, getting even worse . The main question is whether or not the drumming is real, making the Master even crazier . With this revealed, fans speculated on how bad the drumming was during the Master's previous incarnations.
 * Hell, the Doctor himself gets one - Waters of Mars, anyone?
 * Avon of Blakes Seven fame, during the show's fourth and final series. The final straw comes with . Considering what he's been through, the only wonder is it didn't happen sooner.
 * Several survivors of the Zombie Apocalypse in The Walking Dead begin experiencing this from Survivor Guilt or just the stress of dealing with the Primal Fear day in and day out.
 * Major Zod of Smallville's 9th Season started out bad and only got worse from there.
 * From Star Trek: Deep Space Nine, antagonist Dukat. He starts off as a scheming, megalomaniac, yet charming Villain/Anti-Hero, gets gradually worse, especially in season six, until it all finally boils down to this: "I should've killed every last one of them! I should've turned their planet into a graveyard the likes of which the galaxy had never seen! I should've killed them all."
 * Eli Goldsworthy of Degrassi started to become this in the most recent season. First, he reasonably starts to become a little suspicious when a former bully keeps trying to talk to his girlfriend Clare, then he becomes even more possessive of her to the point of being controlling, and she responds by saying she needs some space and that they should take a break. How does Eli deal with this?  of course!
 * Many a character in Oz undergoes this, especially Beecher in season 2 after taking a level in badass. He gets better.
 * from Breaking Bad display this at the end of "Crawl Space" laughing maniacally after realising that
 * Supernatural's season seven does this to culminating in The Born-Again Identity.
 * Several examples in Buffy the Vampire Slayer. Faith, portrayed as not the most stable of individuals to begin with, begins by trying to rape Xander to death and it goes downhill from there. After Tara's death Willow thinks nothing of killing her friends if they get in her way of vengeance, before deciding that destroying the world would be a Mercy Kill. Even Buffy herself is prone to this: the stress of each season finale seems to bring out the worst in her (such as trying to drive her friends away, fleeing from Sunnydale, thinking she can't let anyone close out of fear of getting hurt, then It Gets Worse, oh boy does it ever get worse.

Music

 * Songs about going insane are quite common, actually. Many examples at Sanity Slippage Song.
 * "Stan" by Eminem shows the story of a fanboy with a seriously screwed-up life and a downward spiraling sanity. The video starts with Stan bleaching his hair just like Eminem's, then Stan starts writing letters to him every so often in his room all plastered with posters of Eminem, then he sends Eminem a really pissed off letter complaining about how he missed Stan and his brother at a gig. When his pregnant girlfriend scolds him for wasting his day on watching Eminem, that's the final straw on the back, and he ends up tearing all his posters, tying his girlfriend in his car's trunk, and driving off a bridge.
 * Then Eminem sends back a letter, and starts by apologizing for how long it's taken him to finally respond. Trippin'. Best part: In his response letter, Eminem decides to cite a story he heard on the news about a guy who drove his car off a bridge with his pregnant girlfriend in the trunk, in the hopes that it'll get Stan to calm down a bit. Then Eminem realizes the news story was about Stan. "Damn," indeed.
 * The Nine Inch Nails album The Downward Spiral is a Concept Album that's about Exactly What It Says on the Tin: the gradual destruction of an unnamed man, from the beginning, to.
 * The Violent Femmes' "Country Death Song" is pure American Gothic: rural guy goes mad from isolation and boredom,, then broods over his guilt till...you can probably imagine.
 * Pink Floyd's The Wall chronicles a man slowly alienating himself from the world, causing his mind to collapse on itself until finally what's left of his sanity stages an intervention and forces him to actually deal with his problems.
 * The band's previous albums, The Dark Side of the Moon and (especially) Wish You Were Here, were inspired by the real-life sanity slippage of former bandleader Syd Barrett, who had become impossible to work with. "Now there's a look in your eyes / like black holes in the sky". His former bandmates reluctantly dropped him and felt guilty about it ever after. The two albums were enormously successful, but the subsequent non-stop grind of touring to unappreciative audiences caused Roger Waters to suffer a sanity slippage of his own, which directly inspired The Wall. Which was an even more enormous success! The band more or less called it quits at that point, releasing one more album before parting ways amicably.
 * By Coheed and Cambria's third album, the author in the frame story of their sci-fi epic has started talking to a bicycle and making both death threats and declarations of love to the ex-lover for whom he wrote the story. In the previous albums the author was not a significant character, and the only real sign of his instability was the fact he was writing the kind of material you can make a Prog Rock Concept Album out of.
 * Gorillaz: Both Murdoc and 2D show signs of this as of phase 3, rambling and gibbering like never before. 2D seems a bit sharper than earlier chapters, though, while Murdoc's just gotten bolder and more malevolent.

Professional Wrestling

 * R-Truth turned heel after losing out on WWE Championship opportunity. And after that, his mind.

Tabletop Games

 * A daily occurrence in Warhammer Fantasy Battle and Warhammer 40,000; living in an endlessly terrible Crapsack World will do that. Witches/psykers are especially vulnerable to Slippage, thanks to the source of their powers being the home of The Legions of Hell.
 * As befits its source material, Gaiden Game Dark Heresy has mechanics by which players can go insane.
 * Call of Cthulhu (tabletop game) is famous for introducing the SAN attribute, which drops a little each time the players encounter a monster or cast a spell, or something.
 * Everyone in New World of Darkness, from normal humans to blood-hungry vampires to reality-bending mages, has a Karma Meter. As you slide down the slippery slope, you tend to become a little more unstable with each step, until finally, humans are reduced to raving lunatics, vampires and werewolves go nuts and become meat-hungry animals, mages and changelings fly off the deep end and lose the ability to separate reality from fantasy, and prometheans lose hope of ever becoming humans.
 * The Old World of Darkness also has sanity-slipping Karma Meters, though not all splats have them.
 * The fan-made World of Darkness game Genius: The Transgression is unique in that players start out insane by nature of their profession, and as they lose Obligation start unconsciously altering reality to fit their delusions.
 * Exalted loves this trope:
 * The Solars gradually experience this as they become more and more godlike, from both the Great Curse and general detachment from humanity and less powerful divine beings.
 * Being close to a Primordial War survivor in the First Age can be dangerous, humiliating, and bad for your physical, mental, and social health.
 * Also happens to Infernals. They have access to Yozi Charms. Everything the Yozis are, is made of Charms. Most of the Yozis are insane, and their Charmsets tend to be arranged so that the good stuff with no drawbacks is padlocked by something with benefits that makes you a little crazier. The best example of this is Kimbery, who has an entire Charm tree (built on The Power of Hate) locked behind something that permanently skews the sanity of its user to be either more naive or more vindictive, depending on the chosen variant.
 * In Fading Suns, Psychics and Theurgists are prone to "Urge" and "Hubris" respectively.
 * Characters in Eclipse Phase are very hard to kill permanently due to cortical stacks and backups, fortunately for GMs there's a mechanic called "stress points" that can cause psychological disorders or permanent catatonia if the PC lets them accumulate.
 * Any Killer Game Master worth the title can put this into any game.

Theater

 * Blanche in A Streetcar Named Desire as well as the film adaption with Vivien Leigh.
 * Sweeney Todd: The Demon Barber of Fleet Street does this with the titular character via "Epiphany".

Video Games
""This...isn't...really happening!""
 * (Some of) The characters in Psychonauts whose minds you enter, but especially the ones in the asylum levels.
 * This is a major gameplay element in Call of Cthulhu: Dark Corners of the Earth. The "hero" is slowly going insane due to all the Eldritch Abominations running around. This results in hallucinations, talking to himself, and hearing voices. The player can reduce the rate at which he goes insane by keeping him from being exposed to disturbing situations (this being a horror story based on the works of H.P. Lovecraft, that's easier said than done). If it gets too bad, the hero may attempt suicide and prompt a Nonstandard Game Over.
 * Yggdra Union has, who is quite clearly struggling to stay sane by the end of the game. Considering the particularly brutal Break the Cutie he was subjected to in the past (and how long he's had to live with the trauma), his Sanity Slippage is pretty understandable.
 * Eternal Darkness has this as one of its main gameplay mechanics with a "sanity gauge" that drops whenever enemies are encountered. Once it gets low, the really weird shit kicks in.


 * Sakura in Fate Stay Night. It's like everything anyone ever says to her is another stab at her self confidence. And then Shinji tries . Yeahhhh things kind of go downhill from there.
 * Sid Meiers Alpha Centauri: If you're really kicking the crap out of another faction and refuse to accept their surrender, they send you increasingly-crazy messages until you kill them or otherwise stop the war.
 * In the Paradox Interactive Real Time Strategy game Crusader Kings, characters can occasionally become Stressed. In itself, this only causes a slight stat hit, but if left unchecked, Stress can further worsen into Depression, Schizophrenia, or outright Insanity, and once one of those hits, that character is locked in a vicious spiral of stat decay, personality instability, and possibly even murderous sociopathy until he or she finally dies or gets "Locked Up for Good!" (which is effectively the same thing).
 * This shows up in Borderlands through Patricia Tannis' logs. She starts out sane (if unenthusiastic) on Pandora and the combination of the world's environment and too much time alone pushes her from "Why do I have to be here?" to idle chitchat with someone pinned and dying under a stone pillar because she knows it's the last conversation she'll have with anyone for awhile to dating, then breaking up with, her audio recorder (they're still friends though). All this occurs prior to the events of the game and by the time you meet her she's...a bit off.
 * She also gives a dude named Crazy Earl an artifact to safeguard, and to seal the deal, some of her underwear as well. It was her idea too. Also, Baron Flynt punched her dog.
 * This is arguably the entire plot arc for Atris in KotOR II.
 * And possibly for Bastila in the first game, though the final stages happened offscreen.
 * In a somewhat stranger example, in The Old Republic.  he's broken out by a strike team..... Only to  he spent the better part of the first game trying to destroy?) and  Not that, given his situation, this isn't slightly justified.
 * This plays out in reverse in Time Fcuk. The protagonist is a Heroic Mime, but due to the unusual nature of time and space in the game, he often gets radio messages from his past and future self. In the beginning, you're getting messages from what seem to be several future selves, ranging from a Perky Goth to a Conspiracy Theorist to someone who's flat-out hallucinating. Towards the end, you can hear his early messages, when he was The Everyman—arguably making it scarier, now that you know exactly how he'll be broken.
 * This is the result of the third week of Cross Channel, the first week where Taichi knows and has more of his deep psychological issues surface. If it wasn't for this and the broadcast he makes at the end of that week, this treatment of Kiri would be rather hypocritical and unforgivable.
 * Vampire: The Masquerade Bloodlines featured a quest in which one has to "cleanse" a haunted hotel (much akin to The Shining). Upon finding the diary of a woman whose ghost now lives in the house, one can read her tale of how her husband experienced one of these inspired by romantic jealousy, culminating in him.
 * Kefka in Final Fantasy VI. He was once a general, but he starts disobeying orders and has lost his rank by the time the game's narrative begins. And he just keeps getting worse from there, culminating in the development of a massive god complex and an urge to destroy everything.
 * Fentible of Starship Titanic suffers for these occasional, usually in mid conversation. The end result is mostly rudeness and forgetfulness. Thankfully he can be reset.
 * In Schizophrenzy, you play Private Investigator John K. Facey - a severe schizophrenic. Your sanity is represented by a sort of "health meter" and is constantly decreasing, with only your medication keeping you from going completely over the edge. Of course, even fully medicated you perceive yourself as walking on walls and hallucinate bizarre creatures.
 * In The Sims 2, if a Sim's aspiration meter bottoms out, they'll start doing crazy stuff related to their Aspiration:
 * A Romance Sim will try to dance with a mop...
 * A Popularity Sim will start talking to a puppet made out of a plastic cup...
 * A Family Sim will cuddle a flour sack with a face drawn on it like it was a real baby...
 * A Knowledge Sim will start talking to a volleyball with a face painted on it wearing a mortarboard...
 * And a Fortune Sim will go out on the street and beg for money.
 * Nine Hours, Nine Persons, Nine Doors has
 * Assassin's Creed had mentions of Subject 16, who committed suicide after excessively prolonged Animus sessions caused mental breakdown due to the "Bleeding Effect," where the Animus subject may gain their ancestor's abilities but end up being unable to mentally distinguish themselves from the ancestor, though Desmond only ends up gaining his ancestor Altaïr's Eagle Vision ability. In Assassin's Creed II this is deliberately invoked in an attempt to quickly train Desmond to become an Assassin, but along the way Desmond suffers visual hallucinations and experience (in his sleep) one of Altaïr's memories without being in the Animus. By Assassin's Creed: Brotherhood he's become an Animus-trained Assassin but the hallucinations have gotten more frequent, are now both visual and auditory (sight and sound) and may not even be from his ancestor Ezio's memories. On at least two occasions Desmond inadvertently refers to himself in the first-person when describing Ezio's actions, and later in the game an e-mail reveals that the other modern-day Assassins have heard Desmond screaming in his sleep.
 * Just to make it worse, Desmond is self-conscious of his own growing mental instability, at one point in Brotherhood wondering how long it'll be before he "starts painting symbols on the walls" (referencing Subject 16).
 * The Shadow Hearts games, along with the usual HP and MP gauges, also feature a Sanity Gauge, as the characters are constantly fighting horrific and twisted abominations. If the Sanity of any character slips below zero, the background music changes and the character goes berserk, attacking everything around them.
 * Sergeant Michael Becket of F.E.A.R. 2. A combination of Alma's Mind Rape powers,, and being held captive by Armacham for nine months while being continuously tested and experimented on has driven him gradually insane.
 * Shin Megami Tensei: Devil Survivor has an odd example of an AI apparently undergoing this. The Laplace Mail starts out giving news from the future, but as the game wears on (and the protagonists repeatedly prevent its predictions from coming true), it starts to get glitchier and glitchier, first capitalizing random letters and eventually adding in weird symbols in place of them, changing its "Have a nice day" ending to "Have a nice death", and finally spitting out an error message and discontinuing all together.
 * of all people starts to go crazy in Kid Icarus: Uprising.  It's then defied when
 * However
 * The title character of Iji can experience this, depending on player actions/inactions. She becomes increasingly desperate and maniacal if her body count increases rapidly, going from crying "I'm sorry!" to those she kills to shouting "DIE!", and she swiftly goes completely unhinged if.
 * However
 * The title character of Iji can experience this, depending on player actions/inactions. She becomes increasingly desperate and maniacal if her body count increases rapidly, going from crying "I'm sorry!" to those she kills to shouting "DIE!", and she swiftly goes completely unhinged if.

Web Animation

 * The Resident Evil-inspired video seen here shows Jill clearly on this path after days of fighting zombies alone; ironically, when Nemesis shows up in the second video, having to fight him seems to snap her out of it. (Warning, both videos are slightly NSFW.)

Web Comics
"There. Good as new, best friend! It's like it never happened. No one can ever blame you for dropping him down the stairs now. Stairs? What stairs! Ha ha ha!"
 * Jack from Gunnerkrigg Court. He started off as a pretty normal guy, then he briefly got pulled into a Dark World and saw some very unpleasant things. Since then he became increasingly antisocial, paranoid (at one point he starves himself because he's convinced the Court has laced his food with nanobots to track him) and amoral (compare his treatment of the Laser Cows to his treatment of the Guard Robot). [[Media:Jack Progress 7447.jpg|Heck, even his appearance became worse over time.]] Fortunately, now that he's gotten almost back to normal. Oh, and
 * Vaarsuvius spent most of "Don't Split The Party" undergoing this in The Order of the Stick.
 * Jin of Wapsi Square suffers from a bad case of this after
 * Homestuck--
 * Karkat starts getting shades of this after a particularly brutal Trauma Conga Line.

""This is because, as is now painfully obvious to anyone with a brain, you have basically ""
 * And now Rose is showing signs of it too, now that


 * Garfield Minus Garfield: With no cat to give him sarcastic remarks, Jon Arbuckle slowly descends into madness. Examples include smushing ice cream cones into his face, dressing up for a date... that's in three weeks, jumping in the streets wearing a party hat, chasing cars in the manner of dogs, breaking down sobbing at the most random times, Madness Speak, and, finally, being sent to a Mental Hospital.

Web Original
"LK: [QTE fails and he's thrown to the ground] Are you kid-- Are you-- ... (laughter) Why does-- Why-- Why does-- things not-- Why-- Why do things not do thing why are things in the... things?!"
 * Doctor Horribles Sing Along Blog: Dr. Horrible becomes more evil when his love interest starts going out with his arch-nemesis (willing to kill), and really goes off the edge when
 * Really, it might as well be called Sanity Slippage: The Musical vBlog
 * Deceased Crab starts to ramble like Raocow in the harder parts of his Let's Play videos.
 * His Let's Play of Eversion is his best example of pretending to lose his sanity due to the game's Nightmare Fuel. His blind run of Hell Temple from La-Mulana is his best example of really losing his sanity due to the game's unrelenting cheapness.
 * Speaking of Raocow, he goes in completely the opposite direction. Normally a Talkative Loon, he becomes very... sane and quiet when levels start to grind at him. Some Let's Plays have nothing but angry ranting.
 * For that matter, any Let's Play of I Wanna Be the Guy.
 * Or an unsuspecting Let's Play of Kaizo Mario World. Proton Jon has a particular epic breakdown playing Special 2
 * The epic LP of |Sonic the Hedgehog 2006 by Pokecapn, Medibot, Kung-Fu Jesus, IlluminatusVespucci and John Condit. They played the entire game in less than two days, playing almost non-stop, with only one of them sleeping at any point. Most involved are mildly Cloudcuckoolander-ish to begin with, but as the game progresses, their commentary is filled more and more with non-sequiturs and Cluster F Bombs. A quarter of the way through, they've ordered and consumed copious amounts of General Tso's chicken because it's "full of ideas" (and thus, eating the chicken will give them ideas. It makes perfect sense!). Halfway through, one of them ironically blares out an a cappella version of Flashman's theme at random moments. Three quarters of the way through, they get stuck in the last level, and over the two hours it takes them to beat the level, they can be heard cycling through the Five Stages of Grief (denial, anger, bargaining, depression, acceptance). By the end, one of them is reciting song lyrics in Shatner-esque spoken-word renditions, including "Rocketman", "Fast Car", and finally "Thriller" over the final boss fight. When combined with the slow, melancholic choiral music used in the later stages, it borders on being strangely touching, depending on your mood.
 * It didn't help any that, besides Medibot, none of them got any sleep. Even Medibot didn't get much; the portions of the LP where he's missing don't add up to much more than a catnap or two (and he apparently went home for those, cutting the sleep time further).
 * During Little Kuriboh's LP of Duke Nukem Forever, he gets stuck for one hour on a boss battle over the Hoover Dam. As time and deaths pile on, LK talks about random subjects, goes through many of his character voices, jumbles words together and repeats them ad nauseum. The last straw happens in Part 26 (at 13:00), when he's unable to complete a quick time event needed to kill the boss despite tapping frantically on the buttons (turns out he was tapping the buttons too fast for the game to notice). This makes him laugh maniacally.

"LK: I may have lost my sanity... thank you game... for taking sanity... Duke: Killing you is as easy as breathing. LK: I have five rocket... Did he say killing you is as easy as breathing? What-- it's not! If this is how difficult breathing is BREATHING IS THE HARDEST THING IN THE ENTIRE WORLD! ... Mushroom style... I'm doing this Mushroom Style. Mushroom style all over the place. Mushroom. Badgerbadgerbadgerbadger. Gimme the mushroom!"
 * He then spends most of Part 27 babbling incoherently about mushrooms, badgers, and barrels.

"Oh, I've got a brand-new combine harvester, and I'll give you the key C'mon now, let's get together in perfect harmony. I've got twenty acres, and you've got forty-three 'Cause I've got a brand-new combine harvester, and I'll give you the key!"
 * Pitchfork, the writer of the Rise and Fall of Final Fantasy series of articles, spent the last four years playing though each Final Fantasy game and writing the articles, a rather impressive feat on its own. The zenith was, of course, at Final Fantasy VI and Final Fantasy VII (the former of which got a score of six out of five), but with each progressive game afterwords, he became more divided in his opinion. Then came Final Fantasy XI, which was his first time playing an MMORPG. So not only did he not know what to expect from it, but he didn't realize at first how unrealistic it was to try to "beat" it. His "Vana'diel Diary" gives us quotes like "I refuse to admit that I am not having fun," and he tears the disclaimer given by Square Enix upon logging on ("'THAT BEING SAID, WE HAVE NO DESIRE TO SEE YOUR REAL LIFE SUFFER AS A CONSEQUENCE.' Bullshit. Vicious, brazen mendacity. Like a tobacco company printing "we have no desire that you should develop a dependency while enjoying the smooth taste of our product" on the side of cigarette packs."), and at the end of that, he begs that someone tell him that not all MMOs are like it. In his Final Fantasy XII article, he says that the Final Fantasy under Square is gone forever, leaving only a Cash Cow Franchise Franchise Zombie by Square-Enix. Final Fantasy X-2 seemed to have completely broken his brain ("...so whenever Yuna equips the Songstress job, she not only dons Lenne's clothes but allows Lenne's thoughts and emotions to diffuse throughout her own, causing god this is so stupid why am i"), and Final Fantasy XIII caused him to quit the series entirely.
 * Atop the Fourth Wall: Sometimes, the terrible quality of the comics he's reviewing sends Linkara over the edge, usually with the soundtrack of The Wurzels' "I've Got A Brand New Combine Harvester" (In particular, Dooms IV, Amazons Attack, and Maximum Clonage).

"Gordon: I HAVE TO BLOW EVERYTHING UP! IT'S THE ONLY WAY TO PROVE I'M NOT CRAZY!"
 * "Look at the pretty bunny! Look at the pretty bunny... *Breaks down crying*
 * Common in The Slender Man Mythos. For specific examples--
 * from Everyman HYBRID, Logan from Just Another Fool, Zeke Strahm from Seeking Truth (but he gets saner, possibly) and Damien of ''Dreams in Darkness'. Quite a kettle of fish, is it not?
 * Marble Hornets is essentially made of this and nightmare fuel. Any character that is in front of the screen for several episodes is shown to become either paranoid to the point of obsession (Alex and Jay) or homicidally insane (Masky).
 * In her stay at the hotel, Jessica also appears to succumb to this when she realises that something is wrong.
 * As events progress and he finds himself in increasingly dangerous situations, Gordon in Freeman's Mind is showing increasingly common bouts of uncontrolled rage and paranoia, which is impressive considering his original personality. This was perhaps most clearly demonstrated in episode 29, when he threw a grenade at a large pile of explosive crates.


 * May be a result of playing Kaizo Mario World without save states.
 * Kevin Low from New Game Plus, after countless slights against him, begins to believe the world is against him, as he begins to slip even more, he starts to have spans of time where he wishes vengeance upon his friends. "He smiles at the twitching bloodied body, he knows she is still alive, but he wants her to suffer. She has become a proxy for every single person who hurt him, every situation bent on beating him down. and now they all are suffering. and it pleases him."
 * The Nostalgia Critic went through one during his review of The Neverending Story 3. He started the review feeling scared and hateful towards the film as he does towards most films he thinks that are horrible, then in the middle of his review he goes off on an unusually long (for his standards) Cluster F-Bomb rant over the Character Derailment of the Rock Biter, and by the end of his review.
 * This LP of Super Meat Boy. Hamster seems relatively okay most of the time until he starts dying a lot. Then he devolves into swearing, flailing, laughter that really just says "kill me now" and incoherent gibberish.
 * Mr. Anime, he was originally just a guy who reviewed anime until he went crazy and went on a killing spree killing his family and his teacher.
 * Lanipator's let's play of Amnesia Justine. He plays through the entire game an goes for a 100% completion to get the Easter Egg. After many, many deaths (you have to start from the beginning if you die), he gets to the end of the game and he doesn't seem to get the Easter Egg.  After that, he starts over, kills all the prisoners laughing like a madman and yelling at the characters in the game, and stands next to the last prisoner so that they could die together. Then, when the screen goes black, the words.
 * The Nostalgia Chick snapped completely around "Sleepless In Seattle vs. When Harry Met Sally", kidnapping Todd in the Shadows, tying him to a chair and her twisted mind calling it a date. You wouldn't think it was possible, but she's only got worse from there.

Western Animation
"Buzz Lightyear: YOU SEE THE HAT?! I AM MRS... NESBITT! (laughs maniacally)"
 * Azula in the finale of Avatar: The Last Airbender. Her slippage began with earlier. When Ozai told her to remain in the Fire Nation as Fire Lord, she became increasingly more paranoid. She acted on the paranoia, then began hallucinating, and eventually had a Villainous Breakdown.
 * The Simpsons episode "Springfield Up" contains a very swift summary of how doctor/lawyer Eleanor Abernathy went off her rocker and became the town's yowling cat lady.
 * Frank Grimes learns the hard way that being the Only Sane Man in a Crapsack World is not conducive to one's long term health.
 * Homer himself does so in a Treehouse Of Horror V episode when the cable stops working and they run out of beer. "No tv and no beer make Homer something something..." "Go crazy?" "DON'T MIND IF I DO!" *proceeds to go crazy*
 * Toy Story. Buzz really doesn't take realizing he's a toy well.

"Timon: (comes across a steam vent) Hey! This is home sweet home, baby! Home-- (gets sent into the air a bit by the eruption) Ha ha! Steam! Ha ha! Steam is good. Steam is--is--is water. Whoo! Gotta have water. You know, for the dream home. Steam home, dream home! Steam, steam, steam."
 * Played for Laughs on Jimmy Two-Shoes, when Jimmy is left the only person in Miseryville awake while everyone else is in hibernation. He slowly begins to go crazy.
 * SpongeBob SquarePants and Mr. Krabs try to keep their sanity when they believed they killed the health inspector.
 * In "Pickles", SpongeBob's life takes a turn for the chaotic after a Jerkass customer claims that he forgot the titular condiment. By which we mean he tries to cook his bicycle and hangs the toaster on his front door.
 * Poor Squidward. In between being the entire ocean's Butt Monkey and victim to the constant shenanigans of his next door neighbors, SpongeBob and Patrick, it's no wonder he's been shown to break down into a sobbing wreck or fits of maniacal laughter when the Amusing Injuries and ever-present failures prove too much to handle. In "Squid's Day Off" Squidward tricks SpongeBob into running the Krusty Krab all by himself while he takes a day off, but he keeps imagining SpongeBob destroying the Krusty Krab and repeatedly goes back and forth to and from his house. While taking a bath he hallucinates SpongeBob is watching him and runs off to the Krusty Krab wearing only bubbles.
 * SpongeBob frequently has Sanity Slippage to the point that you wonder whether he's exactly sane to begin with...
 * Mr. Krabs goes crazy when the squeaky noise of the rubber boots he gave Spongebob becomes too much to bear.
 * In Clams after Mr. Krabs looses his millionth dollar we see him slowly go completely insane. The cut back to Mr. Krabs, who begins giggling maniacally and tears his two eyes out, using them as a jumprope is genuinely disturbing.
 * My Little Pony Friendship Is Magic: The Fan Nickname for this is "Cutie Mark Failure Insanity Syndrome", given that a pony failing to live up to their special talent (symbolized by their cutie mark) is the most common cause of ponies going nuts. (It's worth pointing out that in all of these cases, the insanity was cleared up by the end of the episode with The Power of Friendship.)
 * In "Party of One", Pinkie Pie thinks her friends are avoiding her because they're sick of her parties. Her normally curly hair goes straight, she makes her own party guests out of things like a sack of flour and a pile of rocks (whom she holds conversations with), her colourful persona becomes noticeably darker, as if it's under a shadow, and the normally insufferably cheerful pony becomes cranky, miserable, and borderline paranoid schizophrenic. Her slippage even comes complete with Creepy Circus Music Music (which has a disturbing resemblance to the Leitmotif of a certain personification of chaos).
 * In "Best Night Ever", Fluttershy snaps at the Grand Galloping Gala due to all of the animals running in fear from her. After her increasingly desperate methods fail, she goes into full blown Yandere mode, unleashing animal-based chaos with the line "You're... going to LOVE MEEEE!".
 * Twilight Sparkle goes through a complete psychotic break in "Lesson Zero". Convinced that she's about to fail her duty to Princess Celestia, her mane goes disheveled, her teeth grind, her eyes becoming unfocused, she talks to herself, and she starts teleporting at random while undergoing a complete nervous breakdown, culminating in an (unintended) mass hypnosis that requires the Princess herself to intervene, furious at her student abusing her powers..
 * In the King of the Hill episode "Pretty, Pretty Dresses" Bill is very lonely and depressed, and finally loses it when Hank destroys the gifts he'd been saving for his ex-wife Lenore in case she ever came back. He starts wearing her old clothes she'd left behind and talks in a falsetto voice, believing that he himself is Lenore; eventually Hank is able to break him out of it and gets him to get over Lenore.
 * In The Lion King 1 1/2, during a scene approximately taking place during Scar's Villain Song in the original movie, Timon is on the verge of cracking in his "dream home" quest...

"Daffy: (hysterical) Shoot me again! I enjoy it! I love the smell of burnt feathers! And gunpowder! And cordite! I'm an elk -- shoot me! Go on, it's elk season! I'm a fiddler crab -- why don't you shoot me?! It's fiddler crab season!"
 * More or less the plot of Wakfu's Start of Darkness prequel episode.
 * The Christmas episode of Adventure Time shows that, centuries ago, before The End of the World as We Know It this happened to an antique collector by the name of Simon Petrikov after he made the mistake of wearing a cursed artifact. A thousand years of sanity slippage later, the man he was is completely gone, and what remains only knows himself as.
 * Ren of The Ren and Stimpy Show frequently falls into this. Stimpy sometimes does too. And boy is it creepy.
 * Looney Tunes: Daffy Duck seems to fall victim to this a lot. A perfect example occurs in Duck! Rabbit! Duck! after he gets shot by Elmer Fudd one too many times:


 * Animaniacs has this happen almost Once Per Episode to the unfortunate soul the Warners decide to be their "special friend". Most of the time they deserve it, though.
 * Candace from Phineas and Ferb quite often suffers this. Though it's not like she's all there to begin with.
 * Meg Griffin from Family Guy quite frequently out of a desperation for love and affection.
 * Rugrats: From the movie, Tommy totally snaps and almost pours mashed bananas on Dil, knowing the monkeys will be attracted to it. It's thundering and raining the whole time, and Tommy just starts acting more and more crazy as he starts ranting about how much Dil has ruined his life.
 * And in another episode Chaz goes insane in a world where Chuckie doesn't exist.
 * Stu also loses it when he's forced to take care of Angelica after she pretends to have broken her leg.
 * Harleen Quinzel, who would later become Harley Quinn, in the Batman the Animated Series episode "Mad Love".
 * Though he starts out stable, Dib's sanity eventually starts to slip after his attempts to expose Invader Zim for the alien menace he is go unsuccessful for the umpteenth time.
 * The DuckTales (2017) episode "Whatever Happened to Della Duck?" answers that exact question: She's been stranded on the moon after her spaceship crashed, and spending eleven years completely alone clearly starts to erode her sanity. Her first attempt to get home involves building a ramp and attempting to launch herself there, and a future episode reveals she was so desperate for companionship that she got into a staring contest with her own reflection that lasted three weeks. When she finally does manage to get home, she never truly recovers, many fans diagnosing her erratic behavior as PTSD.

Real Life

 * Watching Tom Cruise's career is like watching a mental train wreck in sloooooooooooooooooow motion. Going from a very respected actor to a high school drop out who claims to know more about psychology than people who actually study it is a long fall.
 * Mel Gibson is taking Cruise's slippage and taking it to places few have ever trodden.
 * Which appears to be nothing compared to Randy Quaid and his wife, who are engaging in the kind of folie a deux that leaves TMZ salivating. After bailing on a good number of bills, mortgages, and other outstanding charges, the couple was arrested for squatting in a manor they'd sold years back. And that's when things got really weird, as the Quaids started talking about how most of the recent celebrity deaths were the fault of a hit squad known as the "Star Whackers" that was targeting them and had ties everywhere—in one interview, the couple said the Star Whackers received orders out of a Dairy Queen in Marfa, Texas.
 * Charlie Sheen seems to be a less tragic version. "Tiger Blood" indeed.
 * Howard Hughes inherited a toolmaking company from his father, and built it into one of the world's largest defence contractors during the 1940s and 1950s. He also made a fortune in a parallel career as a Hollywood film producer, bankrolling The Front Page and the original version of Scarface, amongst other hits. His aerospace business produced a string of innovative designs, most of them personally devised - and tested - by Hughes himself, and by the end of Hughes' life the company was successfully branching out into the space industry. But by that time a long-simmering combination of opiate addiction and obsessive-compulsive disorder had transformed him into a recluse, bundled from hotel suite to hotel suite under cover of blankets, interacting only with a small group of hand-picked assistants who were forbidden to look at him. By the 1960s he had completely withdrawn from public life, living on chocolate bars and milk, spending most of his time watching films - in one of his personal cinemas - repeatedly on a loop; if the print he wanted was not to hand he would buy the local TV station and ask them to broadcast it for him. Despite his enormous wealth he eventually died of malnutrition, leaving an emaciated husk of a corpse with broken-off needle tips embedded in its arms.
 * Professional wrestler Randy "Macho Man" Savage was considered a tad on-edge back in the 80's to being just bat-shit crazy in the later years of his life. He was always seen as at least somewhat paranoid (what with threatening anyone who talked to or, heaven forbid, touched Elizabeth). Later there were reports of him carrying a gun with him in his gym bag, as well as him making threats on the lives of just about anyone he felt was impeding his career. His latest decent down the spiral included releasing a rap album and attempting to challenge Hulk Hogan to a real fist-fight. He seemed to be getting better when he died in May, 2011.
 * The Ultimate Warrior, as the documentary Self-Destruction of the Ultimate Warrior will attest.
 * Poor Margot Kidder. In her case, untreated bipolar disorder led to some bizarre antics, such as hiding in bushes naked. She has since been under regular care and says that she's been free of incidents for 11 years.
 * The artist Louis Wain's works became more and more disjointed as he slipped deeper into schizophrenia. He went from painting relatively normal pictures of anthropomorphic cats to painting this.
 * This montage shows the gradual slippage in progress from mildly odd to complete lunacy. Nightmare Fuel warning applies.
 * Pretty much any kind of mental disorder. It starts with something small, but just keeps building up as reality fails to meet one's expectations, and the disorder is increased by the mind to protect itself. The truly hardest part about breaking this is that the whole point of insanity is that the one who is affected likely won't know of his/her insanity.
 * Taken to Tear Jerker levels with people diagnosed with schizophrenia. The symptoms don't usually appear until late teenage and early adult years (16-25), so you could be mentally healthy one moment, and then the next, you gradually slip down the slippery slope towards delusions, hallucinations, mood disorders, and even states comparable to an Empty Shell.
 * Adolf Hitler had this towards the end of his life. A number of causes have been speculated, such as untreated syphilis or drug addiction, but nothing has been solidly proven to be the cause. Possibly, multiple factors combined in an unfortunate manner, for Hitler personally and for the rest of the world as a whole.
 * John McAfee, creator of the eponymous anti-virus software, went from a somewhat eccentric Erudite Stoner type and a genuinely talented software engineer to an increasingly erratic and paranoid wreck (and possibly a murderer) towards the end of his life, courtesy of a combination of several subsequent business ventures going expensively sideways and his lifelong love affair with narcotics.
 * Sometimes, sanity slippage is not that dramatic or serious. Several things can cause temporary reductions in your SAN score. Not having enough human contact, eating nothing but bland meals, never seeing interesting scenery, and other such things can affect your sanity.
 * Sleep deprivation (such as from All The Tropes) can also make you increasingly unhinged hinged hinged hinged hinged ahahaha...
 * Extreme distress, fear, or grief can cause panic attacks and hallucinations.
 * Extreme stress can also cause purely visual hallucinations that the sufferer knows they're not real. The person knows the walls aren't melting, the lamp isn't flickering, there aren't any kaleidoscope patterns spinning through the air. But they're seeing it all anyway and they can't make it stop. The patterns persist even with their eyes closed. Their brain isn't functioning properly and they know it, but there's nothing they can do about it. No amount of rationalizing about how all those unsettling things aren't really happening will make it go away. Imagine knowing that you're standing right on the precipice of insanity and being unable to stop yourself from taking that first step down.