I'm Pooped

[Geonz]

I realized when I felt sleepy after a ride that, in fact, I hadn't had the usual caffeine intake - a glass of iced tea cured it completely. I can kinda tell now when it's real "need a nap" and when it's "have a cup of tea, dear!" time -- but figure specific depletions of any of a number of things could bring on sleepiness, and a nap wouldn't even really help.

[pll]

Mild dehydration can cause sleepiness...