I have advice for prospective patients—if you get sick, your word on its own may not be enough, so make sure that you have some concrete evidence of infirmity, or that your symptoms conform to an accepted pattern. The word “atypical” is pejorative in the medical world, implying one of three things: imagining it, deliberately making it up, or expensive and time consuming investigations will prove it to be benign. We doctors are scientifically trained; we believe that there is an order out there, and if something doesn't fit a scientifically validated pattern, we tend not to believe in it; if the bloods come back normal, it is even harder to persuade us. We're usually right, of course, but not always.

Joe had a new and exotic symptom to add to his catalogue: a feeling of impending doom.

“A frightful fiend doth close behind me tread,” he intoned morbidly, but there were no objective signs whatever.

“All right,” I said, “I'll run a few tests,” knowing I was only postponing things for a few days, but you never know, a few therapeutic bloods might help, and there is always the one-in-a-kajillion chance that something actually might turn up.

Joe returned a few days later. No change, he said; surprise, surprise, I said. Then suddenly he collapsed on to the floor, screaming (in agony, I think, but possibly delight). His abdomen became acutely distended, gouts of blood and acid flew everywhere, quite ruining my new shell suit, and an alien head with the now traditional slavering jaws burst out.

In 20 years of general practice, I've seen everything, so I tapped the key code for “parasitic infestation,” tempted the alien with a few convenient small children, sedated it with intravenous diazepam (finding a vein was a bit tricky), and stuffed it in the surgery fridge, from which nothing ever comes out.

Just then my receptionist arrived, with a sheet of paper. She has seen everything too. “I'll get the mop,” she said.

Joe was still lying on the floor, pale and exsanguinating, but with an annoyingly satisfied I-told-you-I-was-sick look on his face.

“There you are Joe,” I said, waving the sheet of paper at him, “Your tests are completely normal; there's nothing wrong with you.”