I've suffered with insomnia for 15 years and one sure way for me to get sleepy enough to fall asleep is to start scrubbing the bathroom tiles. I know it sounds crazy, but once you've gone without sleep for a year or two, you'll try anything! I've taken all the natural stuff and a couple of non-natural stuffs and scrubbing the tiles has always worked.

Oh, and the pen and paper that lilias suggested works well too