RICE
Tweaked my thumb pretty good at Krav tonight. Got hung up on a pad and bent it back, and I definitely heard something pop. I'm going to ice it, take a little vitamin I, and see where it's at in the morning. If it's bruised and swollen, that's a tear, and I'm off to the doc.
Update: Saw the doctor this morning, and the good news is that it's just a gnarly sprain, with possible damage to the volar plate. The bad news is that gnarly thumb sprains can take a year to heal. Meh.