The first time this happened to me I was 14 & watching a movie at summer camp. I was lying on my back & went to sit up & turned my head to the right. I got a horrible cramp that seemed to go from the upper left back of my neck ( near the base of my skull) up the back of my head. It made my head jerk to the left like something pulled it.The muscle then got very HOT like blood was rushing to it. I had to massage it really hard to stop the pain & it almost gave me a headache. I'm past 50 now & sometimes it happens...like 5 minutes ago...and while painful, it has never been as excruciating as that first time. Sometimes I can internally hear the tendon/muscle move & it feels like one tendon passed over another. I'm an elemenatary teacher & on numerous occasions it's happened to my students. I just tell them to massage it & do yoga neck rolls,which is what I do.