Cannabis raises your heart rate when you smoke it, and that is why you get all jittery and twitchy when stoned...
It doesnt happen as often, but when I get real stoned it feels like im twitching all over. So yes, I know exactly what you are talking about. One way I found to get rid of it is just keep thinking "Its just the drug, its all gonna end soon" and just clear my mind and replace my thoughts with mellowness. Sounds weird but it works good, cuz I hate that. And I know what you mean...