It's even more simple that it at first appears (spoilers)

The mistaken name and thus mistaken operation (which actually didn't happen) and the nightmares in a coma is all very obvious so it can't be what this film is really about. Successful, white upper middle class paranoia is also obvious; ie, the brother who is going to the most violent part of Africa just to help people and the male nurse named Mandingo, a classic slave film name, all obvious. The ending, and realization of the "locked in" syndrome, everybody's worst fear, right, and the imagined window jumping really just his body and mind simply giving up and dying.

All of this is so obvious, I'm thinking that the film and the story is just an exercise in the exploration of fear of hospitals that a lot of us have, often for obvious reasons. What I'm saying is, this is a horror film about fear of hospitals, not a deep psychological film about how one may move through a coma to death.