Informed Self-Diagnosis

Most people, when they fall ill, will only describe their symptoms in general terms ("My stomach hurts", "I think I'm going to throw up", "AAA-CHOO!" etc.) This makes sense - most of us don't have that much medical knowledge, no matter how many doctors / Daily Mail readers think we're all self-medicating with bootleg drugs bought online.

Not so when the patient is a doctor, however. S/he will give a full account of their condition, with all the relevant jargon, even if they're in the middle of collapsing. If they're already in hospital, they will probably be an Annoying Patient, particularly if the other doctors disagree - it's well known that doctors make the worst patients.

See also A Fool for A Client, the equivalent trope for lawyers.

Fanfic

 * In a Bleach fanfiction "Dr. Granz Is In", the second chapter has everyone's favorite pink-haired Espada diagnose himself with apendicitis. He then enlists the help of Espadas 3 through 6 to perform the operation. Noitra leaves early, Grimmjow faints at the site of his organs, and Ulquiorra and Harribel do it all fairly well. Afterall, Ulquiorra was apparently a surgeon in his past life. (Notably, the symptoms and surgery are all realistically protrayed, since the author is actually in medical school and had even just gotten over said disease.)
 * In Forward, Simon gives a self-diagnosis when he gets stabbed in the chest by a pair of scissors when the ship goes haywire. Later on, River gives herself a diagnosis of all of the injuries she's accrued, including broken bones, gunshot wounds, and sunburns.

Film

 * In the first X-Files movie, Scully is stung by a bee and has an immediate reaction. She goes down, describing how she feels - even correcting Mulder when he suggests she's allergic.
 * Although it's not stated or shown in the film itself, there is some probable Fridge Logic behind this: Scully knew Mulder would call 911, but also knew she wouldn't be conscious by the time the EMTs arrived, so she was trusting in him to repeat everything she said to them.
 * Scully also does this in the series with her cancer--the opening to "Memento Mori" had her examining her own X-rays and explaining to Mulder exactly what it was and that she wouldn't live very long.
 * In Predators, Topher Grace's character does this when he gets caught in something akin to a bear trap. He expresses relief that his tibial artery was missed by inches. Royce, an expert in warfare rather than medicine, explains that the trap was meant to maim him rather than kill him, in order to slow down the whole group.
 * In Serenity, Simon is shot in the stomach while trying to assess an injury Kaylee has just taken. As Inara tries to stem the blood flow, he dictates the medication he and Kaylee will both need for their respective injuries. Somewhat justified in that Simon is the only trained medical professional on the ship.

Literature

 * Dr. Maturin, in the Aubrey Maturin series, himself falls prey to a wide variety of injuries and ailments over the course of the series. His self-diagnoses are almost always on the mark, too, though he notably fails to recognize his own addiction to the (opium-based) alcoholic tincture of laudanum.

Live Action TV
"Zoe: "This is really not my area of expertise, doctor. I tend to be putting these into people more than the other thing."
 * Dr Sheldon Hawkes of CSI: NY, having just been rescued from a nasty underwater incident, tells a paramedic he has "a full range of motion - probably just a hairline fracture".
 * Star Trek the Next Generation episode "Arsenal Of Freedom": after Dr. Crusher takes a nasty fall, Picard has to take care of her, and she has to tell him how to do it.
 * During another episode where the entire crew is slowly vanishing and Beverly is the only one who notices, she performs a self diagnostic, mentioning rather tersely that "being the only doctor on board, I had to do it myself."
 * In Firefly episode "Objects in Space", Simon is shot in the leg. Although he's the only medic on board, Zoe has some battlefield first aid experience. As a result, she has to perform surgery on Simon's leg while he stays conscious enough to talk her through the process.

Simon: "You got the bullet. Okay, I'm just going to pass out for a minute, but you're doing great.""


 * Lost "Something Nice Back Home," with a twist. Jack knows he has appendicitis, but won't admit it until Juliet calls him on it, at which point he says his appendix hasn't ruptured yet.
 * Scrubs played with this by having four older doctors all sharing a hospital room. JD is understandably intimidated, but they very kindly inform him of their condition and what's required. Then prank him.
 * Another episode features the "Annoying Patient" angle. Not only does the doctor in question diagnose himself, he brings along a lackey who automatically agrees with everything he says to try and legitimize his claims that the Sacred Heart doctors should just sign off on the drugs he's prescribed himself and let him go about his merrily arrogant way.
 * Obviously, this happens on House quite a bit.
 * In "Three Stories" House prints a graph from his heart monitor, calls a nurse and tells her she has twenty seconds to inject him before he goes into tachycardia. He then crashes immediately, with a surprised "I was wrong..."
 * In the Season 4 finale,
 * House had done this earlier in the finale for himself on awakening with a concussion and retrograde amnesia.
 * House is also able to work out that somebody spiked his coffee with narcotics when he realizes his mouth is dry.
 * Wilson also does this in one of the funniest scenes of the whole series when he realizes House spiked his coffee with amphetamines speeeed! although it's only after confusing Foreman and winking at a patient while he's doing a breast exam.
 * In fact, the whole series does a little too much drink-spiking...
 * Also used in The Greater Good, when a chef's apprentice collapses while reciting her symptoms in big medical words. Turns out she's a doctor.
 * One episode with the pregnant photographer opens with her self-diagnosing a stroke as she's having a stroke. However, as seen below, this is an actual technique for self-diagnosing a stroke that anyone can (and should) learn.
 * In the episode "Epic Fail", a videogame programmer, who complains that his hands felt like they were on fire, uses online resources to self-diagnose himself, which alienates the doctors of Princeton-Plainsboro. However, they soon prove his self-diagnosis wrong. Instead of doing the logical thing and letting THEM help, he keeps trying to self-diagnose and, eventually, get help from doctors outside the hospital. Near the end of the episode he offers a $25k prize for the doctor who solves his case, which he posted online. In an (at first) ironic twist, one of the online doctors DOES solve the case and gets the money. But at the end of the episode, it's revealed that
 * Done in Doc Martin with the "gets it wrong" variant of this trope. Dr Dibbs self-diagnosis almost kills her before Martin manages to correct it. Martin's Aunt Ruth diagnoses herself with a terminal illness, listing all the symptoms, but thankfully Martin is on hand to point a couple of symptoms she's missed which means he has to break the bad news that she is going to live as she has something totally different.

Newspaper Comics

 * In a Dilbert comic, Catbert made Google the new company health plan, saying "from now on, employees must use Google to diagnose their own illnesses."

Real Life

 * Real Life example: The head of the CDC infectious diseases department was bitten by a mosquito in Atlanta. He soon developed symptoms and figured he had West Nile virus. He took his own blood test and confirmed it.
 * Truth in Television, both among physicians and other healthcare professionals. The trick is not to diagnose yourself while you're evaluating yourself. Telling your care team exactly what symptoms you're experiencing can be very helpful; insisting that you have X disease tends to have the opposite effect.
 * This also tends to happen to anyone informed enough to think they have some form of Autism/Asperger's Syndrome, but naive enough to say as much before going to a professional. Combine one such socially-awkward individual with an often ill-informed medical staff who may not recognize all but the most obvious symptoms of Autism to begin with (or even be completely misinformed, such as thinking that only young boys have Autism), and things can get very ugly, very quickly.
 * It really, really doesn't help that the advent of readily-available information on the internet has made self-diagnosing as having Asperger's incredibly popular as an excuse for bad behavior both on and off the internet, as most of the really well-known symptoms make it sound like you're trading the requirement to follow society's rules for a superpower (the fact that most people making this association lack the supposed superpower, ie creative tendencies and high intelligence, is not lost on this troper). Because of this, some people don't even believe Asperger's is a real disorder.
 * Self-diagnosing a stroke is considered good practice by most doctors. Since a stroke will almost always knock you out and there are very few, if any, external symptoms, having someone tell the paramedics or doctors that you had a stroke can save them a lot of time, and save your life. FAST is generally the easiest to remember: Face (half of your face just stops working, and it looks weird), Arms (you can't keep your arms level with each other), Speech (you slur your words as if drunk) and Time (it all happens very quickly).
 * TV Tropes.org: Saving Lives through proper education of self-diagnosis!
 * Being able to self-diagnosis a heart attack is another big one, as they are almost never as big and dramatic as they look on TV.
 * Headache? Stiff neck? Fever? Dislike of bright lights? Get to A&E NOW. People - at least in the UK - are taught this as the symptoms can be sign of meningitis, although they may also be the person having a very bad day. Most TV using meningitis go for the rash-that-won't-vanish-under-a-glass thing, but if you wait for that to appear a. it might not and b. you're often too late by that point.
 * The fact that those are also the symptoms of pretty much any bad hangover can't help. Unexplained bruises are generally par for the course after a heavy night as well...
 * It turns out that stiff neck is the helpful distinguishing symptom. And by stiff neck they really mean it, not the poor approximation that a neck ache tends to be. The test is you attempt to put your chin on your chest. If you can't bend your neck enough to touch your chin to your chest, it's time to seek medical care immediately. Otherwise, it's almost certainly something else less serious.
 * It's more than common for mental health professionals to be suffering from mental illness themselves -- due to either their experience with mental illness is what brought them toward its care or constant proximity to mentally ill people (especially sufferers of PTSD; having the heart strong enough to willfully work with such unfortunate population is a gift). Like all clinical professions, being mentally fit is vital to the proper care of the patients and such individuals should ensure that they stay in one piece. Affective dysregulation can be left unnoticed for an entire lifetime, but being trained to diagnose them can enable clinicians to make actions to prevent them from worsening.
 * While he wasn't the first person to do so, there was an account of a Russian surgeon removing his own appendix while he was stationed in Antarctica.
 * This isn't necessarily limited to the medical profession, either. Professional IT helpdesk workers often have less trouble dealing with complete novices than with people just knowledgeable enough to have made some attempt to diagnose the fault themselves, as the helpdesk people usually have a checklist that they have to follow to the letter and can't simply take the user's word for it if they say they've already tried that, not least because the self-taught user's self-diagnosis isn't as informed as they'd like to think.
 * Alan Alda, hilariously. He reveals in his memoirs that he had intestinal problems while visiting in Chile, and the doctor tried to explain to him what was happening. Alda crisply explained that he knew what was going on and what the treatment was. The young doctor was dumbfounded, and wondered how Alda could possibly know that. Alda explains that he isn't a doctor, bu he played one on M*A*S*H. Beat. The Chilean doctor cracks up, and Alda reflects that he's lying in agonizing pain and still making people laugh without even trying.