Could be hypomania -- a less severe form of mania. Or even depression. I read that waking early can be a sign of bipolar depression. That happened to me. I would wake up around 5 or 6 and not be able to fall back to sleep even if I went to bed late. Check out this article on BP and sleep:
http://www.enotalone.com/mobile/article.php?a=9551

Here's one on hypomania:
http://psychcentral.com/disorders/hy...sode-symptoms/

Hope this helps.