It's very hard to describe what it feels like. It not pain like I'm used to with the Fibro. it like a tingling, numb feeling right down the arm, and it feels really heavy, like I've been lying on it for too long and sort of over the shoulder and itnot eh chest area. Definately not pain, but it makes me very uncomfortable. I've only had it happen 3 times in the past fornight, but not sure what it is. The first time it happened, i had to carry my arm across my body, as it felt really heavy if I left it by my side. I've also got a lot more tingling and numbness in the left hand and wrist. I have always associated this with the Fibro but not so sure now!