What causes weird dreams?

For the past week or two now i have been having some really weird dreams. I woke up this morning in a really weird mood. I could tell i had a strange dream i just couldn't really remember it. But two nights ago i had a dream that i was applying for a job at an insane asylum, and two people, that i have been acquainted with, came up to me and tried to kill me. . Then i took a fire extinguisher and beat them to death. Yeah i know gruesome.Also as soon as i killed them the scene moved to this girl in a red dress laying on the ground and when she sat up all i could see was her skeleton. And it like zoomed out and she was in a music box and i woke up. Also one i remember vividly, I was walking through like a dungeon and we got to this building where we captured red faced demon from insidious (By the way that movie is amazing). And he was trying to kill us all but he couldn't, the only thing he could do was move things in the room we were in. These are the only two that i remember because they effected me the most. Like i said, i have been having weird dreams every night for about a week and a half now. Anybody have a idea why?