muscle spasm
"I developed a muscle spasm in my neck while taking Lamictal. Eventually the spasm did not go away---it turned into an incredibly painful condition Dystonia. The spasm has displaced my jaw and disabled me from being able to work. After developing problems with Flexeril and Cogentin, I was switched to Tizanidine. What a wonderful difference. Though the spasm or pain never stops, it reduced my involuntary movements to the point where they are not obvious, and the pain is also reduced. No bad side effect besides tiredness."