If I ever fall into a coma or become catatonic while I was asleep it is most likely because I had a dream about getting shot in the head, and in the dream I had severe brain damage and am a vegetable.  What I wish for people to do with me at that point is to take me to one of those sleep specialists, and detect when I hit REM after I go to sleep, or induce REM artificially.  Then while I'm dreaming a bunch of people and a doctor have to act like they are in the dream world, so I can hear them, and act like I am getting brain function back.  It might take a while but this is the only thing I see working.  I will then snap out of it once I regain a certain amount of function and I will be able to change back into reality.  This would probably work even in real life if I got shot in the head, to rebuild neuron connections and bring back brain function from mush.