I don't think it's a sleep disorder. It's known in science that sleep deprivation causes multiple physical and mental ailments in anybody. I have always been a chronic sleeper and generally sleep around 10 hours a night. (Which isn't good!) Sleep, in general, is very important to humans. I think it's a symptom, but I don't think it is the cause for the disorder.

((http://en.wikipedia.org/wiki/Sleep_deprivation))