Hi nickO and others, Sleeping on your back, or sides can make the pain in your arms much worse and prevent sleep. What has helped my symptoms, which are in both shoulders and arms, is sleeping on my back with both shoulders propped forward and a little bit up towards my head. I do this with a pillow that extends down under my shoulders, not just supporting my neck and head. If I fall off the pillow, my symptoms recur. If I prop them back up, they resolve. I also make sure my neck is slightly flexed by the pillow being tall enough or second narrow pillow under the very top of my head. All of this positioning makes the scalene neck muscles and the pectoralis minor muscle less taut. Hope it helps you sleep!