muscle spasm
"I was prescribed cyclobenzaprine for numbness and pain in my back, caused by a herniated t3 t4 disc. I had no relief of that pain nor the subsequent pain in the muscles that had been compensating.  After two hours the medication made me so drowsy that I could close my eyes and fall asleep, and could be woken without any concept of time asleep. While awake I was completely unable to concentrate or retain information (I happened to take it while studying, unaware of the consequences). I then slept about 6 hours (3 hours after taking the medication) and then abruptly woke up. Took about an hour to return to sleep. I wouldn't recommend the drug if you are dealing with nerve pain or minor pain."