I guessed the 'twist' of this film in the first minute, because the visual in the first scene mirrors the events of the whole film. That is, a psychologist is drawing a diagram of a person with multiple identities, and crossing out the little circles that represent the different personalities to express his hope that the number will be winnowed down by therapy. And the film, as you will have guessed from this, is an exteriorisation of the struggle for control between competing aspects of a fractured personality. Incidentally, I like books and films where the first scene prefigures the whole. Remember the first scene of Memento, where the film (in this scene only) is literally run backwards, with a Polaroid photo un-making itself.
The genre that I'm talking about, though, is the book or film where the events are a dramatisation of mental processes.
There are lots of problems with this. The theory of multiple personality disorder is probably quite problematic itself. And I can perfectly understand why people would think that a story which turns out to be an internal drama could be just as dreary and unsatisfying as a story where the protagonist wakes up and 'it is all a dream'. Nevertheless I like that kind of story. I couldn't say why.
Here are some good examples. It's not a well populated genre.
Pincher Martin by Wiliam Golding
The Bridge by Iain M Banks
the film Jacob's Ladder
I read a short story by Ursula Le Guin (I think) which was a Star Trek spoof (almost fan fiction). Except all but one of the officers was female, and you come to realise that the writer was dramatising the internal conflict of a woman who has conceived an unplanned pregnancy. ('When we docked with the battle cruiser an alien life form became lodged in the shuttle bay' etc.) it's a funny story. They lock the science officer in the brig for the duration.
When she wrote this story (back in the late seventies I think) it was a fairly new idea. Nowadays I think many people would agree that Star Trek and other TV shows of 'that type' gain some of their audience-mesmerising power from the fact that they exteriorise internal processes by personifying character traits. That may also be why they tend to bland-out into resolution of conflict.
Final questions I ask myself - the degree to which all story-making is of this kind? The degree to which all our experience of the world is of this kind?