That used to happen to me when I first started smoking, but I never smoked a little bit, I always "over-did" it, until I couldn't move and was completely gone from reality. Then, I got used to it, and it no longer happens. Perhaps you should smoke a large amount and get extremely high, a few times in a row, and see if that helps. If not then like others have said, a doctor is probably your best bet, although if he's not MJ friendly he may simply tell you that that's the problem.