There is a definite connection between sleep cycle and mood disturbances. Too much or too little sleep can cause depression and/or mania. Any of the mood disorders can be part of the pattern, particularly seasonal affective disorder and bipolar disorder.

There are some free e-books online by Daniel F. Kripke about light therapy and dark therapy and sleep, but his site seems to be malfunctioning at the moment. Here's a link with some information and a link to one of Kripke's books: http://www.sleephomepages.org/books/brightenlife.html

See if any of that helps. Basically, even though it feels natural (for some of us) to stay up and sleep in, etc., we would have more control and be better off if we would get ourselves onto a regular sleep schedule, and get the right amount of light during the day, and enough dark at night too. I'm nocturnal myself, or at least tend to lose time by staying up a few hours later each night until I miss entire days. It wrecks havoc on my mood sometimes. Light therapy helps to control it. It's not the total answer - therapy is important too.