I am having physio for hip/thigh injury but I don't know how it occurred. My neck muscles seize up frequently for no reason, which can be painful for weeks and now I've done something to my shoulder. It feels like I've pulled a muscle across my collarbone area and it hurts to lift my arm up and move it around. I literally done nothing strenuous or unusual today, just some very gentle physio exercises for my hip. I don't understand it. Does this happen to anyone else? I'm not particularly fit but I'm not inactive either. I'm 39 and feel more akin to 59 recently!