Odd sleep patterns?

During school, i used to go to sleep late sometimes and sometimes i would go to bed at a proper time, regardless i would wake up tired and groggy in the morning and while at school often i couldn't concentrate.

So now that summer has rolled around, at first i would sleep in late like till 11,12 and even 'till 1 and 2 p.m. allot of the time.

For some reason, after a week of that i began waking up earlier and earlier 9 a.m. - 8 a.m and now i wake up routinely between 4:30 - 6 a.m.

Today i actually woke up at 3 a.m.

The strange thing is that i woke up at 3 am today but i have felt alert all day more or less but when i would wake up at 7:30 and go to school at 8 i would be tired and sleep all day. But now that i wake up much earlier i can actually function quite well and i even work on some correspondence courses in the morning.

Any explanation for this?

well, what time are you going to bed? Waking up at 7:30 can be harder than waking up at 4:00 if you are interrupting a sleep cycle.