Ever had DOMS (Delayed-Onset Muscle Soreness)?
It's not a disease, just a normally-abnormal thing that gets better in a few days. Stiffness, soreness, mild swelling beginning about 24-30 hrs. after the exertions.
I've only had it several times over the years, and I know why I have it right now in my calves and quads. It's because I requested 30 minutes of our hour for calisthenics from my trainer on Saturday morning, and he had me doing things I've rarely done. It was hard, but a great workout.
As an experiment, I tried stretching and walking it off for 50 minutes this morning. It didn't seem to do much, but better than sitting, maybe.
Our D-Day post yesterday described 8-hour/day calisthenics for Airborne training (including running). "I thought I was in good shape, but I wasn't." Good grief, that's always the case.