muscle spasm
"I've been using this medicine because I have a very large kidney stone. Unfortunately I'm caught between a rock and a hard place.  If I stop the medicine, passing the stones could be painful. But the side effects I'm having are just about as bad. I have to monitor my food intake because Flexeril makes me nauseous all the time. If I eat the wrong food or don't keep food on my stomach I throw up.  When I was in the hospital I couldn't figure out why I threw up all the time. I'm not on any other medicines at the moment and this has to be the cause.  In the evening, just before I take the medicine again I've noticed the nausea is gone and I start to feel better.  But it all comes back with a vengeance once I take that pill again."