Induced Hypochondria

When a character convinces another (perfectly healthy) character that they are ill, often in order to get them out of the way for a little while, or just to mess with their head. To accomplish it, they may employ fast talking, medical jargon, obviously fake medical devices, etc.; they might even make up a whole new disease. Expect them to say "You don't look so good," or "You're a very sick man."

The victim almost always falls for it, often expressing a desire to "go lie down". May result in Your Days Are Numbered and/or Mistaken for Dying. This trick cannot, however, actually hurt or kill a person like in the case of the Compelling Voice or Your Mind Makes It Real. Typically Played for Laughs. Compare Gaslighting, and You Don't Want to Catch This.

In an inverse, sometimes a fictional disease will be whipped up that has no symptoms and apparently only targets healthy people and is allegedly fatal. This is employed almost exclusively on very gullible people.

A Sub-Trope of Hypochondria.

Examples of Induced Hypochondria include:

Anime and Manga

The manga version of Excel Saga had a chapter in which Iwata was Mistaken for Dying, which ended by revealing that his doctor (and Sitcom Arch Nemesis) had faked his diagnosis. The next chapter started with the team's mentor Kabapu announcing that Iwata had died; the doctor had only exaggerated the symptoms to try to get the case into a medical journal.

Comic Books

In DC Comics, a doctor fakes a medical report to con the Joker into believing that he's dying. The doctor hopes to "scare him straight". Instead, the Joker goes on a final rampage of such hideous scope that it becomes a Crisis Crossover.
- Similarly, Clock King started doing crime because of a doctor telling him he was dying so that his sister could live comfortably when he was gone. However, it turned out that this was genuinely an accident and the doctor was mistaken. As you can imagine, when he got out of prison Clock King tried to kill him for ruining his life.

Film - Animated

In Disney's Pinocchio, 'Honest John' does this to get Pinocchio to go to Pleasure Island.
In Shrek, Shrek and Fiona convince Donkey that he doesn't look so good. They were actually just using him as an excuse to spend another day together, but he's so neurotic that he falls for it anyway.

Film - Live Action

In the 1937 movie Shall We Dance, Peter Petrov talks his nagging manager into becoming seasick so he can go on a date without interference.
The main character of Joe Versus the Volcano is told by the doctor that he's got X days to live, and then some rich guy offers to let him live the rest of his life (what little there is) in luxury, if he will, in return, jump into a volcano and thus mollify some volcano-god-type who's been getting in the way of his Tropical Island Retreat construction-project. It turns out that the doctor had been bribed by the rich guy, and had lied to Joe so that the guy could get the human sacrifice he needed.
In Escape from the Newsroom, several people try to make Ken Finkleman believe he is sick due to exposure to anthrax.
In A Day at the Races, this is the reason Dr. Hackenbush is so well trusted by Mrs Upjohn:

Mrs. Upjohn: Why, I never knew a thing was wrong with me before I met him.

Literature

In The Two Towers Wormtongue has convinced King Theoden that he is far too ill to lead men into battle, possibly with the aid of a Compelling Voice. Gandalf convinces him otherwise.
Used non-humourously in the novel Angel's Kiss. A character gets petty vengeance on an apparently healthy man who slighted him by telling him that he looks ill. He is so convincing that the man goes to his doctor- and discovers he has cancer.
In Mind Games, the protagonist develops a psychic ability that has this effect. She has hypochondria herself, and can get rid of her health anxiety by pushing it into others. This doesn't actually make them ill, but their resulting actions might.

Live-action TV

Happened a couple of times on M*A*S*H as the surgeons used it to get an annoying superior officer out of the way for a little while. Once (possibly the last time they used this device) Hawkeye and BJ got in a serious disagreement, because Hawkeye removed the appendix of a person who didn't need his appendix removed.
An episode of Malcolm in the Middle revolved around the brothers trying to dispose of evidence of what they consider to be the worse thing they ever did: convince their mother she had cancer so she'd be too distraught to get angry at them for their poor report cards.
In an episode of House, House managed to convince an airplane full of people that the symptoms of the disease they already believed they might have caught included things like a spasming left hand. Right on cue, they all starting having those symptoms, proving that they were suffering from mass hysteria.
In an episode of Drake and Josh, Megan somehow tricks Drake into thinking he has a horrible disease that can only be cured by soaking his hands and feet in several gallons of lizard pee.
Leverage, "The Order 23 Job." The team notices a Corrupt Corporate Executive about to go away to Club Fed seems to have germophobia... so they drug his water, send him to the hospital, then hijack an entire wing to make him think he's ended up in the middle of a pandemic.
- In another episode the crew convinces the curator of a museum that he has fallen ill due to a mummy's curse, or at least from fungi in the sarcophagus.
In an episode of Full House, Joey brought home two Counting Crows tickets and Michelle got upset that her sisters would get to go and she wouldn't. Danny made them draw straws and when Stephanie lost, she and DJ concocted a plot to convince Michelle she had the made-up "Shmedrick's Disease" so she would have to stay home. It almost worked until Michelle gave them a heartfelt speech about how she just wanted to go to the concert so she could be cool like her big sisters.
In an episode of Are You Being Served, the staff convince Mr Rumbold that he's suffering from some unspecified stress-related disease, and that he should dismantle the security cameras to save himself from the urge to watch them all the time.

Opera

Bartolo, the Count, Figaro, and Rosina all (for very different reasons) use this on Don Basilio in Rossini's The Barber of Seville.

Video Games

This is a learned skill for the Trickster class, who inflicts status effects by talking to the opponent, in Final Fantasy Tactics A2, referred to in-game as "Sleight of Hand". This includes "Hypochondria", equivalent in effect to poison. Even more insane is the "Suggestion" attack, where they use the power of suggestion to turn the opponent into a toad.
There's a variant in Fallout 2 wherein you can trick a slavemaster into thinking one of his slaves has a disease (made-up and named after your character.) Symptoms include shiftlessness and unwillingness to follow orders. It's highly contagious, so he'd better hand that slave over to you before it contaminates the rest.
- Can also be done while bartering for some slaves (to free them of course!) in Fallout: New Vegas
One puzzle in Strong Bads Cool Game for Attractive People: Strong Badia the Free involves convincing Strong Sad that he has "acute aphasic pretendicitis". Symptoms include uncontrollable shaking, a high fever, and inability to comprehend spoken language (achieved by clever use of a malfunctioning toy, application of a lighter to Strong Sad's thermometer, and attempting to communicate with Homsar, respectively).

Western Animation

Bugs Bunny was fond of this trick, even to the extent of using spotted glasses to convince Elmer Fudd he was "seeing spots".
- "Dr. Devil and Mr. Hare" consisted almost entirely of Bugs doing this to the Tasmanian Devil.
- The Looney Tunes cartoon "The Hypo-Chondri-Cat" takes this gag to its ultimate degree, as mice Hubie and Bertie eventually convince Claude cat that he's dead.
In the DuckTales (1987) episode "The Money Vanishes", the Beagle Boys steal Gyro's latest invention by convincing him he has Inventoritis from being too sedentary, and needs to start jogging... right this instant. He jogs away and they have the run of the laboratory.
In the Ed, Edd 'n' Eddy episode "A Case of Ed", Edd convinces himself that he has a rare and deadly disease, and Eddy decides to take advantage of this for a few cheap laughs. Edd is not amused when he learns the truth
In one episode of Gummi Bears, Cubbi and Gusto end up captured by Toadwart and a pair of ogres. They convince the ogres that they have "gummioleosis", a highly-contagious disease. For added points, they give the ogres a "cure" that involves bathing (anathema to ogres) and scrubbing their chicken pox-like spots (paint) with "one small ogre"...and the two ogres run off chasing after Toadwart.
In one Tom and Jerry short, Jerry painted spots on Tom to make him believe he had measles. Tom eventually finds out and goes after Jerry, but finds that now Jerry had the measles for real.
In an episode of Help! It's the Hair Bear Bunch!", the bears convinced the zookeeper, Mr. Peevely, that he had "zoo-lirium" and had to take a vacation from the Wonderland Zoo.
Classic Disney Shorts brought us "Donald's Day Off", were Donald Duck's nephews prank him into thinking he's sick to the point of soon death. Made hilarious by how Donald is convinced of his "disease" to the point of ignoring logic and reason:

Donald: *walking with his eyes closed* I can't see! Oooow, ooooow! Oh me, oh my *Gets hit with a toy train* Ouch! *Opens his eyes, pushes the train out of the way, and keeps on being "blind"* OOOW, OOOOOW, OOOOOOOW! *Faints*

- In the House of Mouse short "Mickey's Remedy", Mickey Mouse tricks Don's nephews into thinking that they have "Bolvanian Brain Fever" to teach them a lesson after they've taken advantage of him by Playing Sick. He goes as far as convincing them that they have died, and will go to "the bad place" unless they redeem themselves: when Donald returns, he is shocked to find them perfectly well-behaved.
In the The Simpsons episode "Little Big Mom", Lisa is angered by Bart and Homer's slovenliness and convinces them they have leprosy to teach them a lesson.
In the SpongeBob SquarePants episode Mad Snail Disease, Patrick convinces Squidward that Squidward has the titular disease, kicking off a panic in all of Bikini Bottom. Slightly unusual example in that Patrick isn't trying to get rid of Squidward; mostly he seems to enjoy the attention and the fact that people listen to him and treat him like an expert.
In the South Park episode "Bloody Mary," Randy Marsh drives drunk and gets pulled over and prosecuted for a DUI offense. Part of Randy Marsh's sentence for his DUI is enrollment with Alcoholics Anonymous and their twelve-step program. At first, he is only willing to confess that he "really like[s] beer," but the AA members not only push him to say that he is an alcoholic, but Randy begins to compulsively drink alcoholic beverages, convinced that he is an alcoholic. Hilarity Ensues after this, culminating in Stan convincing Randy that he is indeed able to control his alcohol consumption, restoring the status quo.

Newspaper Comics

In Dilbert, Dilbert convinced Stan the Marketer that he had altered his DNA through his computer. Being a marketer (whose career is built upon unverified consumer anecdotes), Stan actually believed him and started growing whiskers and a cute little nose. Eventually Dilbert "cured" him by saying a report taken out of context from an unrelated focus group said he wasn't changing after all.