Exhaustion: Strange Things That Happen to Your Body

It's been about an hour since I had coffee and if this were any other morning, I'd think I needed more to perk me up, but all I have to do is look in the mirror to know it's not a lack of caffeine, but rather exhaustion. When I get super tired, I get big black circles under my eyes and my face gets really splotchy.  Almost as though I've got windburn.  Makeup doesn't begin to cover up these signs my body gives me that I'm exhausted.

I've heard of strange things happening to people when they're tired such as twitching eyes or minor bouts of vertigo.  I'm curious- what does your body do to let you know you need to recharge?