muscle spasm
"I took Flexeril because I had been feeling intense back muscle pain. I was told that it would make me sleepy and feel relaxed. I took it at 9:00pm thinking it was going to kick in quickly! I was wrong, 15 minutes later nothing! So I made dinner went online, then out of nowhere my neck felt heavy like I couldn't hold my head up and I stumbled to my bed. I saw the clock and it showed 11:00ish. I  slept like a baby! Woke up feeling great the next day well rested and my back felt better."