Because the next night, my knee went crunch.
Ironically, it didn't do this during karate practice, though I did do it at practice. We did mostly kata, which for me means Kusanku (plus review and minor teaching). All that popping up and down for Kusanku, and my knees were fine for all of it. Not even a twinge. Twinges are actually pretty common for me when kneeling all the way down, which happens no fewer than six times in Kusanku.
No. It was sitting down in the car. Opened the door, started to sit and crunch! It took me several tries to get my leg bent enough to get it inside, and driving home was no fun at all (stick shift).
I don't seem to have done anything really problematic to the knee. Today it's sore and swollen, but it functions fine and is perfectly stable. I've broken out the soft brace and ice packs, but don't see a need for the hard brace this time. But between the bruises from Tuesday (mostly forearms) and the limp, I seriously look like an abuse case. Based on past experience it should be fine in about four days. It rather puts the kibosh on Sensei's extra Sunday practice (at least for me), but I should be back in action by the next regularly scheduled class.
But I think I'm going to skip the full kneels for a few classes.