I really liked the mushroom-idea! *spoilers*
That the main guy kept tripping while he was being tortured to death gave this movie an added sense of cruelty. When he imagined that he got away just to being pulled back to reality, i thought that was brilliant.
It reminded me of some recurring dreams in had when i was a kid. For example: Sometimes i wanted something so desperately (doesn't had to be material, could also have been something like a friendship or a job or a good mark or similar stuff) that my mind tried to give me the most vivid dreams of exactly that thing i wanted... which always lead to a huge dissappointment when i woke up and realized that it was not real.. it's hard to describe. Really liked that feeling of hopelessness that this movie delivered.