I have noted that the times I wake up early like that were preceded by significant stress the previous day. In fact, that is what happened last night and today.

I got worked up in response to a stressor and it became very difficult to go to sleep. I had difficulty staying asleep as well. The days before were also stressful and my sleep wasn't the best.

An event doesn't necessarily have to be unpleasant for it to be stressful, but merely be highly activating. I think a lot of bipolar is just that the stress placed upon our bodies exceeds it's ability to repair and maintain. That minor mood swings and recurrance are preceded by a physiological cascade failure and the cognitive dysfunction and deficits we struggle with further compromise our ability to cope; to keep our mind/body in balance and have appropriate responses to stress. At least, in my experience things like sleep, exercise, and diet can have a significant impact on stability, all of which actively promote homeostasis in ways that no medication can replace.

To be clear, the above is just a brief overview of what I believe leads to unstable moods.