Hi Emre,
I put my money on that it is a primarily a conditioned response. It is as if your mind (the child) is protesting. 'why the hell do I have to endure this uncomfortable situation'. The superego is afraid that the cold will create problems, et voila, they actually are created. Fear will make everything worse. Also the soothe factor is mostly absent when it is cold and grey. The last couple of weeks I've experienced some symptoms that had been gone since last winter, as many others did too. You are simply in a worse mood than when it is sunny and warm outside.
It is natural to pull up your shoulders and tug in your head, like penguins bend their head to their chest to loose less heat in an icy storm. The muscles that are used most have the biggest potential to create problems, in this case the area you described. The problems will also linger when you 'have' TMS, whereas in others any discomfort from tugging isn't created, and if it is it rapidly disappears. If you follow Sarno's theory, it is indeed the little lack of oxygen to the area that is to blame. But the trapezius and other upper back muscles are famous anyway for getting spasms and becoming painful in stressed people.
I personally had a conditioned response from cold. Whenever I went outside my legs started to get weak. It still happens sometimes, but the fact that the weakness wasn't consistent helped me believe it is a conditioned response. When I am relaxed and mellow, no weakness. When I am already stressed and moody, the weakness returns.
take care and take your time
Giga