Drink a tea or hot chocolate, or imagine myself into one of my usual sleep fantasies. I've done it ever since I was small. Generally, the scene is that I've been captured and confined in a space (so not moving around lots, which in conducive to sleep). Favourites are: kidnapped and locked in an old-timey carriage, in a zoo-like cage, a mermaid caught in a ship's hold (this one's real good coz I have to keep my legs together like a tail, haha). Anyway, I just think about how much I can't move and so in my fantasies I'm clearly somewhat bored so the main thing for the captured mermaid to do is sleep away the hours. Somehow it's often easier for me to fall asleep in a role than just as my sleepy self.