Secretly Dying

A character knows His Days Are Numbered and tries to keep it under wraps. If he's diagnosed with The Virus or an Incurable Cough of Death, Herr Doktor may be begged or ordered to keep silent about it. If he's harboring a Secret Stab Wound, he may wear extra shirts and haphazard bandages to avoid a Mortal Wound Reveal. This may invoke Fridge Logic of the Stupid Sacrifice variety if medical treatment could have prolonged the victim's life.

Why? Perhaps he doesn't want his friends treating him with kid gloves or passing the Despair Event Horizon, or he wants to spend his last days seeing his sweetheart smiling rather than grief-stricken. Alternately, he might want to keep his enemies from getting a morale boost out of it, especially if he's engaged in a Thanatos Gambit. It can also be a selfish act if his condition represents a danger to others, such as with The Plague or a Zombie Infectee.

Very much Truth in Television, some people prefer normality if they're dying. Also, many terminal diseases such as cancer and AIDS used to have (and in some cases still have) huge stigmas attached to them. Political figures often need to do this, otherwise The Revolution Will Not Be Civilized.

This may lead to Dying Alone, if taken to its logical extreme.

'''This is usually a MAJOR Plot Twist. The examples section is a minefield of unmarked spoilers.'''

Anime and Manga

 * Roy Fokker's death in Macross. After coming back from a mission where his fighter got shot up, he spends a quiet night at his girlfriend's place strumming his guitar... then keels over, revealing bloody wounds in his back. Possibly a Stupid Sacrifice since the injuries weren't severe enough to debilitate him—he might have lived if he'd gotten immediate treatment.
 * This incident is referenced and the trope subverted in Macross Frontier, where Ozma Lee goes to Ranka's concert while seriously wounded and collapses - but he's rushed to the hospital and survives.
 * In Dear, Subaru's Evil Hand is painfully consuming him. He keeps quiet about it so Komomo wont worry.
 * In Trigun when Wolfwood is mortally wounded in his battle with Chapel, he speaks briefly to Vash, then heads to an abandoned church to confess his sins. Vash is too busy angsting about his own duel with Caine the Longshot (who ended it via suicide) to notice the trail of blood droplets in his wake.
 * In Darker than Black season 1, Huang hides a Secret Stab Wound to sacrifice themself as a distraction. Also in DTB, November 11 believes Amber's precognition that he's not long for this world, but keeps it to himself.
 * Also in Darker than Black, Amber spans a Batman Gambit to detonate the Gate using judicious use of her time manipulation power. The price she pays for using her power is Cast From Lifespan in reverse, causing her to age backwards. She worked it all out so that she had exactly enough lifespan left to see her plan to fruition, and unmakes herself the last time she uses her power.
 * In Gundam Seed, Rau le Creuset is very slowly dying because his cells are a good 30 years older than they should be. There are a number of scenes that show him self-medicating to deal with the pain, but the cause is not explained until The Big Damn Reveal, as his condition is the root of his misanthropy and thus his desire to wipe out humanity with him in retaliation.
 * Kaiser in Season 3 of Yu-Gi-Oh! GX. He wants one last amazing duel before his heart condition takes him down, and he shrugs off concern and support all season when anyone notices the pain he's in.
 * In One Piece, Hiruluk keeps his fatal illness secret from Chopper. After getting Shoo the Dog, though, Chopper learns the trurh by listening to Hiruluk and Kureha.
 * In Naruto, had a fatal illness.
 * Fairy Tail:
 * In Shigofumi there was the story of an older man watching over a little girl named Mikawa (the same as the protagonist). The older man treated the girl nicely, but did not tell her that he was dying from a condition. He ultimately dies by pushing Mikawa out of the way of a bus, though he gets hit and dies.

Comics

 * In Transformers: Last Stand of the Wreckers, Ironfist is dying from taking a cerebro-seeking bullet to the head in an "accident", and having it slowly working its way closer and closer to its target and unable to be stopped. He hides it because he's assigned to what is a dream mission for him and doesn't want to be ruled unfit to serve it.
 * All-Star Superman begins with Superman discovering that he's dying. The comic ends with him telling the world in the form of a Clark Kent article.
 * All-Star Superman begins with Superman discovering that he's dying. The comic ends with him telling the world in the form of a Clark Kent article.

Film

 * One of the most famous movie examples is in El Cid, when the eponymous hero tells those around him to keep the fact that he is dying a secret so as to avoid demoralising the Spanish troops and boosting the morale of the besieging Moors. This ends with the famous scene when the now-deceased Cid, strapped to his horse, "leads" his army out of the city gates to victory.
 * Tony Stark in Iron Man 2.
 * At the end of Once Upon a Time in the West, Cheyenne reveals that he's bleeding out from a gut-shot. He asks Harmonica to get him out of sight from the new town before he keels over.
 * In Shaun of the Dead, Shaun's Mum doesn't let anyone see their zombie bite to avoid worrying anyone. This leads to the movie's biggest Tear Jerker when Shaun has to kill her when she turns.

Literature

 * Near the end of the Harry Potter series, Harry learns that Dumbledore had been hiding an unbreakable death curse from destroying a horcrux.
 * In The Curse Of Chalion, Cazaril has a supernatural tumor in his gut haunted by the ghost of the Complete Monster he killed with magic. He tries desperately to keep it under wraps, both for political reasons and so the girls he's trying to protect won't worry about him.
 * In The Dogs of War, has been diagnosed with cancer.
 * In The Dresden Files book Death Masks, exchanges himself to almost certain death for Harry. Harry learns via a letter that was arranged beforehand that his benefactor was already dying from cancer.
 * In the Gaunt's Ghosts novel Blood Pact, the reader is led to believe that Ayatani Zweil is dying of cancer this way. He isn't:.

Live-Action TV

 * Star Trek: The Original Series episode "For the World is Hollow and I Have Touched the Sky". Dr. McCoy learns that he's suffering from a disease called xenopolycythemia which will kill him in one year. When he tells Kirk about it he asks him to keep it to himself so he'll be most effective in his job in the time left.
 * Professor Arturo on Sliders had an incurable disease which will kill him in a number of months, but didn't want anyone to know.
 * from Heroes hides the fact that he has cancer from everyone at the start.
 * President Laura Roslin spends most of the first season of the remake of Battlestar Galactica hiding the fact that she has terminal breast cancer from the fleet at large. Then, after the news broke, and a miracle cured her, it came out at Baltar's trial that she was hiding a relapse.
 * During the early part of season 7 of The X-Files, Mulder is hospitalized for unusual brain activity. At the end of the three-episode arc, it's implied he made a full recovery. In reality, he did not and is dying from an "undiagnosable condition." He hides it from everyone, including the audience. It's not until he goes missing in season 8 that anyone finds out. And how do Scully and Skinner find out? Doggett has the manhunt team bring in his family headstone from North Carolina, which Mulder had recently changed to include his own name, birth year, and anticipated year of death.
 * Given how hard it was for him to deal with Scully's illness and its terminal diagnosis back in season 4-5, it's no surprise he wanted to spare her that suffering.
 * In the last season of Star Trek: Deep Space Nine, Odo conceals from Kira (with whom he's recently gotten together after many seasons of pining) the fact that he's got the disease that's infected his entire species. Slightly subverted in that Kira is actually perfectly aware what's going on; she just doesn't let on because she respects Odo's reasons for not telling her.
 * Firefly: Word of God says this is why joined Serenity.

Theater

 * In Act Five of Cyrano De Bergerac, Cyrano tries to keep his mortal wound from showing to his beloved, Roxanne.

Video Games

 * Proto Man from Mega Man knows that his power supply is flawed and will eventually run out of energy. He'd prefer to not tell others about it and just accept when his fate will come.
 * In inFamous 2, Zeke catches The Virus and hides it from Cole until Cole's powers allow him to plainly see it.
 * Shinjiro Aragaki in Persona 3 is slowly killing himself with power-inhibiting drugs. He refrains from mentioning his poor health to anyone, mostly because he's expecting one of two other things to kill him before the side effects of the drugs manage to do it, and because he thinks he deserves it. Even when it comes out that he was taking the suppressants, he waves off any concerns about the side effects, and only comes close to hinting how little time he has to the female protagonist in the last few stages of his Social Link.
 * Also the Protagonist themselves go through this in the good ending. After perfoming a Heroic Sacrifice, s/he is just living to meet up with everyone on graduation day, like they promised. However, everyone in SEES has forgotten about what they've accomplished, even if they haven't forgotten about you. Only one person remembers and she makes sure that you won't die alone. Unless you're playing Portable with a New Game+, then your preferred Love Interest can spend your last few seconds with you.
 * Hanbe from Sengoku Basara hides his tuberculosis from Hideyoshi and Mitsunari, who know he's ill, just not that it's terminal. If they were aware they'd probably either lose hope and abandon the conquest of Japan, or force him to stop being The Strategist.
 * Comes completely unexpected in Metal Gear Solid 4: Guns of the Patriots with Naomi Hunter, who reveals it just after she disabled the implants that extended her life for the last couple of years, and dies within the next few minutes, having completed the last thing she needed to do.

Real Life

 * Admiral Yi Sun-Shin died this way, suffering a mortal injury due a chance shot during the Battle of Noryang. Witnessed only by three people, his final orders were to press the attack home and to hide his death from the crew and fleet, to avoid ruining morale at a critical moment. His final victory was thus won posthumously.
 * Bill Hicks never told anyone but his doctors that he had cancer until he died from it, just weeks after his last live performance.
 * One version of the death of Turkish Sultan Murad I at the Battle of Kosovo in 1389 is that he was killed in his tent before or during the battle by a Serb pretending to defect, and asked his entourage to make sure the news didn't get out to his army. Unfortunately for colourful historical tales, there are other versions in which he is killed fighting during the battle or even afterwards.
 * Freddie Mercury kept his AIDS diagnosis secret within Queen and a few close friends, not publicly revealing he had AIDS until the day before he died.
 * Pete Postlethwaite allegedly averted this trope on the set of Inception, telling Cillian Murphy that he was dying.