Conventions that suspend reality: 1 Injury and illness

There are some conventions in popular fiction that are so well-established that we don't even notice how much they defy real-life experience unless we sit down and think about it.
My favourite is the knock on the head.  There are any number of books, films and television programs where the hero is knocked on the head, and, after a spell of unconsciousness, climbs to his feet, defeats the bad guy, and gets the girl--or, alternatively,  where he knocks a couple of bad guys on the head, who get up a bit later, rub their skulls, and set off in hot pursuit.  Nobody blinks at this--despite the fact that in real life we regard being knocked unconscious as a very serious matter, one that requires a trip to hospital and an X-ray and bed-rest.  We know very well that head injuries are dangerous, but we do not apply that knowledge to the world of fiction.
Of course popular fiction has a strange attitude to illness and injury in general. Try to imagine James Bond catching a cold!  Infected cuts, conjunctivitis, piles, diarrhea and the other ills that flesh is heir to are, I am sure, found far more frequently in real life than in fiction. Even more interesting is the way characters are unimpeded by injuries which I, for one, would find disabling.  I have to take the evening off if I have a tooth out, but some heroes can scale a cliff after being shot through the shoulder--and, of course, operatic sopranos and tenors can sing gloriously while suffocating to death or dying of tuberculosis.
There are, of course plenty of books that deal honestly with injury and illness and make every effort to get medical details right.  What is strange is that the books which don't get away with it so easily.  The world of these books is, after all, ostensibly our own--but we don't apply our own rules to it, and usually don't even notice that omission.