Too tired to sleep?

I don't know if it's some primordial part of our brains that makes it so difficult to go to sleep once you've gotten past that magical barrier of sleep deprivation. You know the one I'm talking about. Your eyes feel really fat and dry, your thinking becomes sluggish and blurred, and yet, even if you were to lay down right now, you'd still be wide awake.

Or, maybe it's something far more sinister. Like the simple fact that continuing to drink tea this late just drugs up my brain and makes it misbehave.