Dear Welcome to HCM We understand your concerns I went through your details. There is no reason that weed smoking can cause numbness on your right arm. Over and above, your numbness goes off when you do some physical exercises. As you suspect, the problem is just in your mind. When you obsess about hand being numb, that happens. Don t worry. If you require more of my help in this aspect, please use this URL. http://goo.gl/aYW2pR. Make sure that you include every minute details possible. Hope this answers your query. Available for further clarifications. Good luck. Take care.