Funnily enough, I have exactly the same problem as you. I woke up with a pain in my neck in February which hasn`t gone away so I had an MRI scan about a month ago which didn`t show up anything. Around the time of the MRI, my pain went into my upper arm and I am convinced it is caused by a problem with my shoulder (possibly to do with the ligaments) I can put my arm above my head and around my back. I can`t put any downward pressure on it though, as it hurts like hell. It really hurts in bed at night. I tried hitting it with a course of ipruprofen which helped until the drug wore off and then I was back where I started. Your only course is to go to the doctor for a proper diagnosis. I might try the physio at work (faster than waiting on the NHS) and then I will probably do the same.