hugs ster. I would ask the pharmacist. How often does it happen, is it within a certain amount of time after taking your daily med? Is it possible that the medicine is helping you beging to relax, and you are holding your muscles so tight you haven't realized it etc? Most meds do have side effects (in fact, in some ways, what the medicine is intended to do is a (side) effect!) But anything out of the ordinary, can be scarey. Does the medicine paper insert talk about something like this? (Or check it online at the drug maker's website.) TC