Claustrophobia

Small enclosed spaces. Like bee stings and heights, this is one of those things that unnerve essentially everybody, but, like those two, it also affects some people much more than others. Some people are deathly afraid of enclosed spaces, and anything from being trapped in a stuck elevator to being shut in a closet could cause them to Freak Out and make being Locked in A Room and Locked in A Freezer ever so much more fun for all involved. Studies show that around 1 in 20 people in the world have severe claustrophobia. For fictional characters, the number is more like 1 in 3. Expect visions of small places getting smaller and smaller until there's no place to breathe, and expect anyone who is revealed to be claustrophobic before the fact to be put into a tight situation eventually.

If this is The Hero's debilitating weakness, then it's also an example of Why Did It Have to Be Snakes, though it is a phobia that can and will occur in any kind of character, since it's so easy to give situations where it would come into play.

Anime and Manga

 * Mendo from Urusei Yatsura suffers from both this and a fear of darkness... unless any women are watching, in which case his desire to look cool and suave trumps it. It's later revealed that he developed these phobias as a child from the actions of
 * The normally cheerful Tanpopo in Imadoki! freaks out when trapped in an elevator by a hacker. She later reveals that her fear of dark, small spaces is due to.
 * The Enigma of Amigara Fault will give you this.
 * Ash Ketchum's Pikachu from Pokémon is actually implied to be claustrophobic because of his dislike of being contained within a Pokeball like all of the other Pokemon. The only time we ever see him come out of a Pokeball was at the very beginning of the first episode where Ash chooses him as his starter Pokemon, and the only time we ever see him go inside a Pokeball is about halfway through Pokémon the First Movie during the scene where Mewtwo captures all of the trainers' Pokemon using several sinister-looking Pokeballs (which for some reason, also capture Pokemon that are already inside their own Pokeballs), so he can create an army of cloned Pokemon to help him rule the world. When the aforementioned "Clone Balls" come back to release all of the captured Pokemon, Pikachu, as a result of this, is apparently now extremely pissed...

Comics

 * Storm of the X-Men is traditionally claustrophobic, dating back to Chris Claremont's work on the comic. A rocket attack that killed her mother also left her buried in rubble for hours with the body. She keeps it under control except in similarly extreme situations. She also has this phobia in certain adaptations, particularly X Men the Animated Series and X-Men Evolution.
 * Atari Force. "Okay, what genius decided to put a claustrophobic man in space?"

Fan Fiction

 * In the Homestuck fanfic "four titles", John air and wind powers have a side-effect of giving him claustrophobia--he detests anything but open air.
 * Shows up quite a bit in Tin Man fanfic. Justified there because the Tin Suit was pure hell for Cain, DG was trapped in a coffin during the series and came close to not surviving it, and Raw was about to face a nasty end trapped in a Papay cocoon.
 * In Neon Exodus Evangelion, DJ Croft is afflicted with this. It proves debilitating when he's trapped in the elevator with Misato, and downright crippling when he's stuck in the Dirac Sea.
 * In YuGiOh! Soul of Silicon, Ebon Magician Curran has this, leading to her wanting revenge on her owner for keeping her card in a box.

Film

 * Woody Allen in Manhattan Murder Mystery gets trapped with his wife in an elevator, and cries out in panic: "I'm a world-renowned claustrophobic!" Then trying to escape they discover a murdered corpse on top of the elevator's roof: "Claustrophobia and a dead body - this is a neurotic's jackpot!"
 * In the first live action Teenage Mutant Ninja Turtles movie, Casey Jones is revealed to be claustrophobic when taken to the turtles' lair in the sewers.
 * The tunnel-digger in The Great Escape was claustrophobic. At first it seems sort of weird or funny, but then we see this big tough guy curled up in the fetal position in a business suit, waiting for some Nazis to pass by...

Literature

 * The most recent Artemis Fowl book gives Holly Short claustrophobia tied to some newly revealed backstory, although she never seemed to have a problem with small spaces in previous books. This is explained away as that she had overcome this claustrophobia long before the events of the books, but her body had become that of an adolescent due to unforeseen side effects of the time traveling, so she had gotten back her claustrophobia.
 * Main character Robert Langdon from The Da Vinci Code and Angels and Demons, due to being trapped in a well in his childhood.
 * In Rowan of Rin by Emily Rodda, weak and cowardly Rowan is fated to accompany six big, strong, brave villagers up the forbidden mountain to find out what has stopped up the village's stream. The big, strong, brave villagers get picked off one at a time due to phobias and fears. One of the last to go is Marlie, the stout little weaver, who tries valiantly to fight past her claustrophobia, but can't do it. She's forced to turn back. Lucky, too, because the last leg of the journey is a three-day stretch inside a winding tunnel so tiny that even little Rowan is crawling on his stomach the whole way, and Strong Jonn can barely fit. And they can't take any supplies.
 * Yago from Remnants. He fell into a construction hole in his backyard during a rainstorm, and wasn't rescued until the next morning.
 * David Eddings' Belgariad
 * Silk and Malloreon develops a pronounced case of claustrophobia after Relg rescues him from a pit by carrying him through- as in, right through- the rock it's carved out of. Up to that point he had only minor difficulties with it when he was in the cave system of the Ulgos.
 * Relg himself suffers from the opposite fear -- agoraphobia, the fear of open spaces -- at first. He had lived his entire life in the caves of Ulgoland, and had not only had never seen the sky, he had no real concept of "sky", "sun", "clouds", or "stars". Garion spends several days just trying to keep him vaguely functional.
 * In The Talisman by Stephen King and Peter Straub, Wolf, the Territories werewolf who has befriended the hero, is violently claustrophobic, to the point that he refuses to ride in a small car.
 * Phase, of the Whateley Universe has some degree of claustrophobia. This is pretty reasonable, since he's: been experimented on (i.e. tortured) by a Mad Scientist while trapped in a box the size of a coffin; nearly suffocated underground; been trapped in a pitch-dark sewer with no flashlight while being attacked by a zombie army; and his own powers mean he can pass through solid objects but he can't see or breathe while he's doing it. Ouch.
 * In Bedlam's Bard by Mercedes Lackey, a claustrophobic character gets locked in a decompression chamber as a form of torture.
 * Inverted in Isaac Asimov's Robot Trilogy. In The Caves of Steel Protagonist Elijah Baley and all of the Earthlings raised in the crowded, claustrophobic Cities, have agoraphobia -- a fear of open spaces, in this case the outdoors in general. Baley starts confronting this fear in the second novel, and is largely successful, although being caught in a thunderstorm doesn't help.
 * Played straight in Nightfall. The people there are so afraid of dark that 15 minutes without light are enough for a 10% chance of becoming extremely claustrophobic.
 * Asimov himself was a claustraphile - he worked best in small, enclosed spaces.
 * In Animorphs, the entire Andalite race is claustrophobic. Justified in that Andalites are descended from herd animals that lived in grasslands.
 * In The Ellimist Chronicles (a distant prequel to the main Animorphs series), the Ketrans have a similar species-wide claustrophobia. This is seen when they are forced to enter and fly an alien ship of opaque metal. Ketrans are a winged species which live on massive transparent crystals that float in the sky.
 * Rand Al'Thor develops claustrophobia after being abducted, stuffed in a trunk, cut off from channeling, and shipped off on a trip of hundreds of miles, only being allowed out for minutes at a time for weeks.
 * In Margaret Mahy's Maddigan's Fantasia and Maddigans Quest, the TV series written by the same author, Eden the boy magician has this fear, which is useful to the plot because he is the only magical character and his absence in some scenes forces the other characters to think for themselves and get out of sticky situations without magic.
 * Allie in Devon Monk's Allie Beckstrom series

Live Action Television
"Ed: *slap*
 * The UFO episode "Sub-Smash" has a female Shado crewmember who's morbidly claustrophobic. She's none too happy when she has to try escaping from the crashed submarine of the title through a narrow missile tube. She's even less happy when it fails to open, leaving her trapped inside. Her commanding officer also suffered from claustrophobia, and originally thought her crying for help was his own mind starting to crack up.
 * Garak the Magnificent Bastard from DS9 has a major case of claustrophobia that becomes a plot point on several occasions of the show. Also a case of Real Life Writes the Plot as the actor suffers from acute claustrophobia and it was an issue for actor as well as the character when filming the episode that reveals the condition.
 * Star Trek Voyager. Tom Paris apparently suffers from this subconsciously, causing him to frequently crawl out of a Human Popsicle tube in one episode, much to the annoyance of Seven of Nine who had to keep putting him back in.
 * Lister in Red Dwarf had a bout of this when performing an Air Vent Passageway escape. Lampshaded the fact that it was the first time this had ever come up. He explains that he's fine so long as he knows he can get out. He developed the phobia
 * One of the many phobias of Monk. Subverted in the episode where he was.
 * Barbara Bain's real life claustrophobia was written into an episode of Mission Impossible in which her character (also claustrophobic) is tortured by being drugged and held in a small, enclosed space.
 * In one episode of Night Court, Dan Fielding reveals his claustrophobia while trapped in a stuck elevator with two sumo wrestlers and bailiff Roz. She helps calm him by having his close his eyes and imagine he is standing in the middle of a football stadium, with lots of room all around him, and it's filled with happy, cheering people who are all looking at him...
 * In season 10 of ER, it's revealed that Neela suffers from claustrophobia when she has to spend a few hours in a hyperbaric chamber with a baby with carbon monoxide poisoning.
 * The Mash episode "C*A*V*E" has Hawkeye having to deal with this when enemy shelling forces the 4077th to relocate to a nearby cave. The same episode has normally tough-as-nails Margaret Houlihan admitting to a deathly fear of loud noises.
 * Anya from Buffy the Vampire Slayer was revealed as claustrophobic in the Season Six episode when the cast were trapped in Buffy's house.
 * In Stargate Universe, the normally tough-as-nails Greer turns out to be claustrophobic, just before going into an underground tunnel network.
 * Doctor Reid Oliver from As the World Turns showed signs of severe claustrophobia when the elevator he and Luke were in got stuck, going so far as to risk damaging his hands in an attempt to escape and manhandling Luke in fear that Luke's jumping could genuinely get them killed. Seeing as all he had to do to escape death by train was wiggle out of his seatbelt, open his door (possibly break the window and exit that way if the door also refused to open), and sprint, this could have been an Authors Saving Throw. However, the actor played the scene as calmly frantic rather than as if claustrophobia was severely impairing his judgment.
 * Sonny Corinthos from General Hospital has severe claustrophobia; its origin is because his abusive stepfather Zeke used to lock him in a closet, and it has been used to excuse Sonny getting away with his litany of crimes because prison would be too much for him to take.
 * Mike Cannon in Las Vegas has claustrophobia(he even says that it's part of the reason he's a valet; he can spend most of his time outside). When a power outage seals Mike, Ed and Mitch in the security room, he begins to lose it, leading to Ed being confused because Mike has by this point begun to spend a lot of time in the security room; Mike explains that as long as he knows he can leave, he can control it, then this happens:

Mike: Mr. D...you slapped me.

Ed: Well, Mike, I had to do something, you were freaking out.

Mike: Well, I'm still freaking out, and now my face hurts."

"Vila: I'd be glad to [crawl through the service shaft], it's just I've got this problem with enclosed spaces. There's a medical name for it.
 * Vila Restal of Blakes Seven, though IIRC this was never mentioned again. As a thief he must have seen plenty of small hidey-holes, so let's just assume that Vila is scared of everything.

Jenna: Cowardice?"

Tabletop Games

 * In Dungeons and Dragons, Avariels (winged elves) are often depicted as suffering from claustrophobia as a racial trait.
 * One of the many horror tropes invoked in Innistrad:

Toys

 * Gums of the Werebears toy line is claustrophobic and transforms when he's in a small, dark space.

Video Games

 * The titular Prince of Persia reveals in the first game that he is claustrophobic, or at least he's "not comfortable in tight places."
 * Carla Valenti in Fahrenheit. Notable because in two levels, you actually have to guide her through claustrophobic environments, simultaneously controlling her movement and her breath. If you fail the latter, she freaks out and the game's over.
 * In Ace Attorney, Edgeworth definitely has a debilitating fear of being stuck in elevators; Fanon is split on whether this is elevator-specific or if he doesn't like any small spaces.
 * In Grim Fandango, French waiter Raoul is claustrophobic, and Manny has to lock him up inside a closet.
 * It's never explicitly stated, but in Final Fantasy VII, Cloud freaks out the times in the game he's forced to go into a tight space, like when he goes into the hut to open the bridge on Mt. Corel or has to enter the submarine interior. Considering his history, it would make sense for him to be a claustrophobe.
 * Two unavoidable instances of this in Escape From Horrorland. One is where you are crawling through incredibly cramped wooden tunnels while being chased by a mummy at high speed directly behind you, and it is very easy to get lost in the tunnels. The other time is when you have to shut yourself inside a coffin and use it as a boat down a sewer, while spiders enter the coffin and try to bite you.
 * Charlie Cutter, in Uncharted 3, is dangerously claustrophobic.

Web Comics
""At least I'm not claustrophobic. Not that I should think about claustrophobia right now... oops.""
 * In Sluggy Freelance Zoe is able to give herself a panic attack in a dark tunnel through trying not to think about it.

Western Animation

 * Garrett on Extreme Ghostbusters is claustrophobic, and has to confront his fear when facing a ghost that makes people's phobias come to life.
 * Sparks on Sealab 2021 goes into panic attacks when he and most of the cast are trapped inside the janitor's closet.
 * Hawkgirl in the DCAU is claustrophobic, as shown in "Just A Dream." She hyperventilates when trapped in a holographic box by Luminus, which foreshadows her nearly having a heart attack when Dr. Destiny traps her in a coffin in an unescapable dream.
 * In Avatar: The Last Airbender, Appa is seen to have a great dislike for enclosed spaces, especially being underground. Makes sense, considering that he's a large animal who is used to flight.
 * In SpongeBob SquarePants, Squidward tells SpongeBob and Patrick that he is claustrophobic. However, SpongeBob and Patrick think that means he was scared of Santa Claus. Complete with Patrick trying to "scare" him by saying "Ho ho ho!"
 * Jessie Bannon from Jonny Quest the Real Adventures is claustrophobic, conveniently presented in an episode where her and Jonny end up stranded in an underwater laboratory with only a bunch of deadly mutant fish for company.
 * Dizzy is revealed to suffer from this in Roughnecks Starship Troopers Chronicles. It becomes a problem when The Squad has to recon a series of bug tunnels known as "Bug City".
 * James Rhodes from Iron Man developed claustrophobia as a result of drowning while wearing his War Machine armor.