I feel that one's consciousness or spirit is always experiencing something in some form or fashion... However when we enter altered states (such as the sleep/dream state), there is the question as to whether or not one's memory of what was experienced is integrated into one's waking memory...
For example - have you ever woken up from a night's rest with no memory of having had any dreams the night before? Then some time during the course of the day either something jogs your memory or you just suddenly and unexpectedly recall the content of dream from the prior night's sleep?
I have read in some OBE literature (particularly Robert Bruce's book) that there are some issues with memory integration following OBE experiences... That it's possible to have had an OBE and fail to integrate the all the details of that experience upon reconnection with the physical body..
I'm not well-versed in those types of experiences but I often have the sudden dream recall happen to me after remembering nothing upon initially waking...
So I suspect individuals in comas are consciously experiencing something - but when they physically wake up there is the question as to whether or not they can access that information/memory....
It's a really good question though and one I have pondered before myself....
