"If you should die before you wake..."

I just had the scariest dream I've ever had in my life. Check that. This wasn't a scary dream. This was a full-blown nightmare. I haven't had one of those since I was twelve.

I am WIDE a-fuckin'-wake.

What causes nightmares? I am going to research this in an effort to make myself stop my stomach from feeling like it's on a rollercoaster.

***UPDATE***

According to Wikipedia, a small demon slipped in through my keyhole and sat on my chest. I don't feel a lot better yet.