Sleepiness Explained

Why is it that at the end of the day, or when you get tired your brain feels fuzzy?  Perhaps I'm the only one who gets that way, but it seems the harder I try to focus on whatever it is that needs my attention, the more impossible it gets to think clearly.  Maybe it's because there are little people inside your skull who jump up and down on your brain all day.  Then at the end of the day your brain is numb from all the stomping it received and therefore struggles to keep a continuous, coherent stream of thought.  Now I know what you might say, what about when you wake up feeling groggy?  The answer is quite simple. The little people did not stop bouncing throughout the night while you were sleeping, ergo your brain received a bruising all night, making you less alert in the morning.  A simple remedy for this is caffein.  It works for those little folks in the same way as chloroform does for us.  And when it wears off and the little hoppers begin to stir you feel sleepy, groggy, or fuzzy again.  Just a thought I had.