A Puzzling Sleep Pattern

Often I feel sleepy in the afternoon, suspect that I may not be getting enough sleep at night and resolve to go to bed earlier. Yet, as bed time approaches, I feel wide awake as I potter away on the computer. If I compel myself to go to bed before about 23:30 I usually wake up every couple of hours or so during the night, while if I defer bed till midnight I usually sleep through the night until around 06:00, and sometimes don't wake till my alarm wakes me at 06:50.

How strange !!