If you've been unable to sleep for a while, the best advice I've ever been given is to leave the bed for at least 15 minutes. What I usually do is go to my living room, lie on the sofa and read a book or something. After around 15 minutes I go back to bed and give sleep a try.

It never works out to lie sleepless for extended periods in bed, so just accept the fact of your sleeplessness and do something else for a while.