I'm not sure if this is the same as what you're talking about but when I smoke I can't keep my body still. I don't shake but my muscles do get tense and contort some. I roll all over the bed, I stretch out, I get into funny positions, my hands sometimes grab the sheets or clentch up or sometimes my whole body goes straight like a plan. This only happens on big doses not small ones and I don't have much control over it. During breakthroughs I have no idea what's going on, I might be moving or I might be still ? I'd have to set up a camera to see what was happening but once I'm aware of my body I'm all over the place until I slowly relax