I originally posted my story around 2 years or so ago and this is therefore an update.
Nothing has changed in my case after many years of suffering at night. Doctors are a waste of time as they tell you that you are the only person in the world to have this problem. Well they should visit this website.
My own conclusions are that there must be a trapped nerve in my neck or left shoulder area. I say this because it is definitely worse if I use weights above my shoulder, play golf or even after massage. All of these things are applying pressure & stress to the shoulder/neck area so it is reasonable for me to conclude that a nerve issue is the prime cause. Additionally, like many people I sit in front of a PC all day and therefore posture is very poor. I believe all of this has contributed to the problem. In fact a physiotherapist warned me many years ago that I would suffer if I did not improve my posture.
I am now going to try wearing a back/shoulder brace. I have tried a brace previously but it was too small and therefore I did not give it a fair trial but I could see that it certainly stopped the slouching over the PC.
I have been on a muscle relaxing tablet for around 6 years and have tried to get the dosage reduced over the past few months. I have now reduced the dose by 75% and sleeping is really difficult but I am coping OK. I will update you if the back/shoulder brace makes any improvement.
Regards from the UK