Pardon me...
True story: my father kept a jar of Grey Poupon in the glovebox of his car for years because of this ad--because one never does know.
One measure of fatigue.
One way I know I've worn myself out: though there's much to be done, and though I'm even interested in doing it, I gradually become unable to get to it, to stop looking at random, stupid crap, or to go to sleep--any one of which would be an acceptable option at this juncture. It's probably a good thing that I'm cutting myself more slack than usual this semester.
