Right after I have a really strong orgasm, the left side of my lower abdomen tenses up in a charley horse-like cramp. God Damn it hurts like a mother-fucker! But it also feels good in this weird, masochistic way.
(It's from having 3 c-sections..the ligaments supporting my uterus don't stand up to the test of some strong orgasmic contractions. But I guess it's worth it because I'm still tight as the first time. *grin*)