Leifmk
Deity
Try Jacob's Ladder.
Very cool movie from back in the eighties. Definitely has the nightmare and twist part down perfect, no real escape or the ultimate escape depending on your perspective.
It's from 1990, actually. And it was the first film I would have mentioned in this thread, except that the big revelation comes at the very end so it kind of fails to match the OP's criteria. It certainly is nightmarish as hell.