ex·haus·tion (g-zôschn)n.
-- The inability to respond to stimuli; extreme fatigue.
-- The act or an instance of using up a supply of something.
-- The extraction of the active constituents of a drug by treating with water, alcohol, or another solvent

Coffee is a stimuli, and I am unable to respond to it currently. Therefore, I am exhausted. 4 straight days of all-day meetings in Northern Virginia have made my eyelids heavy, and my desire for a nap intense.