I play lists in my head. Some favorites are:
* Name 50 Beatles songs
* go through the alphabet naming TV shows that begin with that letter, but I can't repeat the same show. For example, if I said "Brady Bunch" for B, I'm never allowed to use Brady Bunch again. I've used this game so many times, I fall asleep wracking my brain for As and Bs
*Name 50 household items that are actually brand names... Qtips, Kleenex, Windex, Frisbee, Walkman, Rollerblades, etc.

All are silly games but I always fall asleep fast while thinking them through. I don't believe I ever got to Z on the tv show name game.

I also have a story idea in my head for a murder mystery. I have the characters all worked out. Who did it, how, etc. But I'll never put it to paper (mainly because I don't have the talent or inclination) but its a darn good story, and I've been falling asleep to it for at least 5/6 years. It changes every so often too... started out as a love story after my boyfriend asked me what I'd consider the ultimate romance novel. Then I got dumped, so it turned to a muyrder mystery! LOL At any rate, I still fall asleep making plot twists and surprise discoveries.