check this site out:
http://www.all.org/issues/eol07.htm
None of us knows what is going on inside the head of comatose or minimally conscious patients. They may appear to be near death, and then revive. They may show agitation, then relax and sleep then wake up lucid. I would never stop feeding and hydrating a patient who was able to breathe on his own. If I were told that my spouse was brain damaged beyond recovery, and if she was deteriorating before my eyes, I would honor her desire for me to take the time I need to mourn her then let her go. She would do the same for me. We have discussed this more than once, we are both nurses, and we have had to make this decision with regard to parents. We still miss them, but we believe they have gone on before us to a better place.