Do I have a sleeping disorder?

I generally cannot fall asleep unless I am sleepy (I accomplish that with about an hour of comic book reading). I usually go to sleep between 4am and 5am. Almost every single day, I wake up at around 9am or 10am (I suspect it might be because of the screaming kids at my next-door neighbor’s daycare center). I’m too tired to stay up, so I go back to sleep.

From that point on, I sleep very fitfully until around noon. Tossing and turning, switching sides, putting pillows over my face, etc. I know I’m getting deep sleep in bursts (because I’m dreaming), but the bursts last only 20–30 minutes (the fact that I consciously wake up, switch sides and rearrange pillows and then continue my dreams still astonishes me).

The question is: am I struggling through fitful morning sleep because of my sleeping schedule? Is it just the noise and light bothering me?

4am to 12pm seems to be my natural circadian rhythm. Whether employed or not, whenever I don’t have to be somewhere the next day, I always seem to fall into this pattern. Mornings have always been rough for me, even when I’ve had enough or close to enough sleep. I’ve tried switching my sleeping schedule many times, but I always fall back to 4–12.

I exercise regularly and eat pretty healthy. I rarely drink coffee. What else could be disturbing the second half of my sleep?