So I wasn't terribly surprised to read the following:
"as you slept, your body also lost water in your breath, through your pores, and during any bathroom visits. First thing in the morning, your body may be down 20 ounces from normal hydration levels. Failing to replenish right away sets you up for dehydration and a disastrous race or workout."- Loren Cordain
So I guess it's not just the two martinis or the bagel with brisket for dinner :) We are naturally dehydrated when we wake up - and if you don't drink some water first thing, you'll spend most of the day trying to catch up.
Tomorrow morning, grab a big glass of water on your way to the shower and top off the tank!