I have seen a lot of films and TV shows where one of the characters is injured and they are always being told that they must stay awake and not fall asleep. Is it really important somebody not fall asleep when they are injured or is it just another TV device that is used to increase the drama?
A little of both. 
I’m sure the medical pros will weigh in on this soon, but my understanding is that they don’t want you falling asleep right away if there’s any danger of a closed head injury, make sure there’s no concussion or second impact syndrome. They don’t want you checking in and then checking out, so to speak.
your humble TubaDiva
Could this be related to Cecil’s latest column?
Funny how the question always seems to be answered just when you ask it.
While this certainly answers some of my questions although it doesn’t answer if the person is losing conciousness for some other reason such as a blow to the head.
I suppose if a lay person was with somebody who was losing conciousness it would be simple to see if the injured person was still alive if he was awake. If the injured person fell asleep and their breathing slowed down then it would be easier for them to stop breathing without other person noticing so maybe there is a slight advantage to stopping them from falling aslepp.
The context in which I am familiar (not personally) with this warning is in cases of drug overdoses. When the patient has taken a large number of… say… quaaludes, if they were to fall asleep their body’s metabolism would slow even more and be unable to fight off the effects (death).
Here’s another idea: I’d imagine that a patient’s ability to say how they feel – or even just moan at appropriate times – would be very helpful for the first medical professionals on the scene.
I asked my wife about this once (she used to be a nurse) and she said that it is pretty standard to try to keep injured patients conscious; not only because it is easier to monitor them that way (and possibly gain information about what happened, where it hurts etc), but also because falling into unconsciousness brings about real physiological changes in the patient; the blood pressure drops, breathing switches over to automatic (and if the ‘automatic’ bit is damaged, that’s a big problem), hormones like adrenaline, normally stimulated by processes connected with consciousness, stop being squirted into the bloodstream.
In short (she says), allowing the patient to lapse into unconsciousness may tip them over the edge into a spiral of decline from which recovery is less likely.