From Psychology Today How to Get Great Sleep:

Everyone has a troubled night sometimes, or even a run of them, which happens to the average person about once a year. It's part of being human, subject to stress and worry. But it's what we do in response to it, experts say, that determines whether we will wind up with chronic insomnia. It turns out that the best thing to do in response to a bout of sleeplessness is often, well... nothing at all.

(via Lifehacker)