To add to all that, the excercises I did on Sunday were a lot more strenuous than I am used to, and included a lot less general stretching. As a result I am sore in place that I forgot existed. We did like 150 squats (something I never do) and my thighs are so sore that I can hardly walk up and down a flight of stairs. In addition, my neck is sore from Ne-Waza, and avoiding the chokes of that highly-competitive Sensei.
My wife laughs at me - she asks why I pay money to put myself in pain - she's willing to hurt me for free. She just doesn't know how good it feels.