I remember seeing this movie around 2008, and it was an English movie, but not necessarily from the U.S. A few parts I remember from the movie was that:

1. The main character had migraines or something, and I’m not sure but I think maybe every time he had a migraine he went somewhere else (not the Butterfly Effect).
2. Either the main character or someone else was trying to remember how they got to this place, and he remembered they were having a meeting in this kind of wooden meeting hall. Something wrong happened and he, or someone else ended up killing everyone in the meeting hall.
3. The main character and another girl ended up having sex in a small shack while they were trying to hide from something. Then either they jumped to another location, or either the guy or girl changed into something. At least, something bad happened after they had sex.
4. I remember a lot of the scenes took place in a forest, but they jumped to different places too, and some were very dream-like.