My last pottery session left my fingers drumming on the kitchen counter for hours. I get that same twitchy feeling, like the clay is still moving under my skin. For me, it's definitely in the muscles, especially after wedging a lot of clay. I found that soaking my hands in warm water helps settle them down. Otherwise, I just lie in bed feeling every little tremor, which is no good for sleep. Sometimes a heavy blanket on my hands weights them enough to stop the jitters.