If I'm trying too hard to get to sleep, and fretting about it affecting my performance is making it worse, I recall what one of my colleagues told me.
He was cycling at high altitude in the Himalayas (his idea of a break from work!). The altitude meant that he couldn't breathe properly and kept him awake in his tent, yet he had to be fit to cycle each day.
He just repeated to himself "this is body-rest, this is body-rest". I do this now - it calms me down, and makes me feel that my body is getting rested even if I am not actually sleeping.
