Sleepy time

It's strange how the context of what I need to do during the day makes me more or less tired when it's time to get up.

I went to bed at 9:45 last night. Pretty normal when you have to get up at 5:45.

I woke up at 3:30am feeling pretty refreshed and well rested, then went back to bed for a little "finishing touch" sleep.

So how, I ask, is it possible that I end up dead tired and almost miss the bus because I couldn't drag myself out of bed when the alarm goes off.