I went to the doctor and got it x-rayed. I guess the radiologist can't take a look at it until tomorrow. The doctor said that she herself doesn't think the foot is broken, based on the x-ray. But, there's some weird stuff going on in the ankle, which could either be from the time I sprained it in high school, or it might be a bone chip. So she said to just keep my weight off it until tomorrow.
As to what happened, I don't know. Heck, my brother saw it happen and he doesn't know either. One second I'm walking down the stairs, the next, I'm falling right off them, missed three stairs on the way down, and then landed on the floor. My feet got caught under me and bent back. My other foot is also painful, but not like my left one is.
After I crawled myself to the couch, I actually laughed out loud because it was so ridiculous. I just...fell, for no discernable reason.