Inexplicable energy levels.

This is a topic I don't think I have addressed much of at all... but I have certainly had the question in my mind on many occasions: If I have been up for nearly 20 hours(or whatever lengthy span of time it may be), have been very physically busy for much or all of that time, why is it that I am not totally crashed out in the deepest slumber my body can manage right now?

I don't even know how to speculate on this sort of thing... maybe since I have almost always been at a loss for the way to properly describe the way my energy cycles seem to defy logical reasoning.  In my research about sleep I have found that waking at the proper time during your nightly sleep cycles can have a significant effect on how easy it is to actually get up.  I don't remember learning much about how it affects the overall energy level for the day as a whole, though, and I tend to think diet might have a greater role in this topic anyway.

In any case I really need to be sleeping soon.  I have a very busy day ahead of me tomorrow and I want to make sure I am performing in tip-top shape... which would be better than tip-side or tip-bottom shape I guess.