Layperson speaking, but I think that can happen with inflammation. When I had my fall, I was almost fine that day, slighly worse the next day, and on crutches by day 3. Not sure why it took a while to swell up, but it did. I'd strongly advise really taking care of yourself and limiting activity and seeing if that kicks it into healing mode.

I would say do ice and anti-inflammatories religiously for a few days, no biking, no KNEE CHAIR, elevate it, try to stay off it, and see if that helps. If not, maybe it's go to the doctor time, kiddo.

Hope you feel better- let us knoe how you're doing.

-Amy