Maybe it’s the same thing I recently had. After running a half marathon in April this year and cycling another 20km from and to the course, I also had some weird muscle cramps when finally taking a rest. It was almost like something was crawling under my skin. My muscles felt like they were cramping together and releasing very quickly and very locally in tiny spots all over my calves. It was such a surreal feeling. Kinda creepy and weird, but at the same time also kinda nice and satisfying.