Weird sleeping problem

[VaeVictis]

Some people just require fewer hours of sleep than others:
http://www.livescience.com/5638-people-sleep.html

Additionally, getting eight hours, while optimal on average, is useless if you're tossing and turning all night. Eights hours is an average, and individuals may require more or less.
I don't think you have a disorder per say (so says a random person on the internetz), but you may want to find a way to regulate your sleep cycle.