Meine Theorie ist ja: alles drei ist wahr: er ist verrückt, liegt im Koma *und* ist in der Zeit gereist. Detailliertere Argumentation gibt's hier zu besichtigen: http://domeofstars.com/forum/index.php?topic=1223.105 (Seiten 8 und 9, evtl. noch folgende - weiß nicht mehr so genau.) Auszug:

Of course, there is another intriguing option here for explaining the entire dialogue. If we trust our ears before our eyes, what we're left with is this:

Sam: Who are you?
Crane: I'm your worst nightmare.
Nurse?: What are you doing? - Aaaaaaa!
Crane: I'm gonna kill you, Tyler.
Nurse?: No, Sam! Aaaaaa!

Now, what's striking about this dialogue is how well it works if you remove Crane's lines from it completely:

Sam: Who are you?
Nurse?: What are you doing? - Aaaaaaa!
Nurse?: No, Sam! Aaaaaa!

This leaves us with a delusional Sam hearing an imaginary voice and attacking the nurse or whoever it was that was approaching him. Which would at least take care of the question of how Sam can be speaking at all: if he's not in a coma but insane, there needn't be anything that keeps him from speaking. Evidence for this interpretation could be the fact that Crane's voice sounds very different from Sam's and the other guy's - a lot more like something that *could* be just inside someone's head.