On one level I am aware that I haven't gotten enough sleep, but when my mind would ordinarily start getting foggy and my eyes would start drooping, the tired feeling remains very far in the background, something I can note and then ignore. There is none of the giddy, twitchy, jumpy feeling I used to get when I drank caffeinated beverages. And in fact, I've more or less completely stopped drinking them -- caffeine's side effects become much more noticeable when you have something better to compare it with.

Where caffeine prevents you from going to sleep, Provigil stops you from *wanting* to go to sleep. Big difference in my book.

All animals sleep, despite the huge evolutionary advantage if one did not have to sleep.  This suggests something ancient in the biology of the brain requires sleep.  Even fruit flies need sleep.

The researcher who pointed this out thinks it's simply the basic chemicals needed by neurons which cause the problem.  The bloodstream can't deliver enough glucose and nutrients to meet the demands of an operational brain.  Apparently it can to other neurons, but not to a brain.

So sleep is simply a time when the brain is slowed down and operation altered so neurons and glial cells can be recharged.

This explains a lot about sleep deprivation.  Visual hallucinations, starting with the "bug flickers" in peripheral vision as the motion-sensing systems malfunction.  Altered thinking and states of consciousness.  And death if the autonomic systems malfunction.

In humans, 48 hours can often be achieved by prepared individuals.  So I'm not surprised at easy enhancement of the quality of 40 hours in young military men in good condition.