Take anyone with a psychiatric disorder and the chances are they don't sleep well. The result of their illness, you might think. Now this long-standing assumption is being turned on its head, with the suggestion that poor sleep might actually cause some psychiatric illnesses or lead people to behave in ways that doctors mistake for mental problems.

http://www.newscientist.com/article/mg20126962.100-are-bad-sleeping-habits-driving-us-mad.html?full=true