Depression definitely disrupts normal sleeping pattern/rhythms. Most doctors will ask if you find that you're waking up early in the morning. Lately, as the days get shorter, (I'm way up here in Toronto, CA), I find myself waking up before it gets light and I feel wide awake and I think it must be time to get up and I don't have a clock I can see from my bed. So, I get up, turn on the kettle and have a smoke. Then I look at the clock and it's 3:30AM so I try and go back to sleep. I usually manage to get a few more hours of fitful sleep and get up around 7:00AM. But then, at about 1:00PM or 2:00PM I am exhausted and I just have to lay down for nap. Then I find that that is when I reach real deep REM sleep with full-on dreaming and I'll wake up at like 6:00PM. This is a regular pattern for me when I don't smoke pot. Oddly enough when I have pot I start smoking it with my coffee in the morning. Just tiny amounts throughout the day. Then, I sleep through the night and I don't nap during the day at all.
Here's a lecture on the topic of depression that speaks to this disrupted sleep pattern. http://www.youtube.com/watch?v=NOAgplgTxfc
I want to find a spot to start a thread about this video.