I've had obsessions before. Just the other night I literally stayed up all night because every time I tried to fall asleep, horrible images would pop into my head, and I couldn't make them go away. A lot of stuff dealing with death. This is actually a symptom of obsessive compulsiveness (my dad's a psychologist). I wish I could help you more, but I really don't know how to make them go away (otherwise I'd actually be able to sleep). One pattern I do notice is that the obsessions get worse when I'm stressed out. Some ways I get rid of stress are running, writing, listening to music. And just getting out of the house with friends helps a lot. If it really starts to interfere with your normal lifestyle, see if you can find a professional to talk to. Good luck!