I would have thought sleeping on your right side was a bad idea as it would be likely to close the thoracic outlet, but then again if you don't get symptoms overnight then it may not be so bad. Sleeping on my side is a definite no no for me and everytime I do I wake up with symptoms. Slleeping on your back is probably best (with a pillow tucked under your knees to support your lower back) as long as your mattress isn't too soft. If you can't sleep on you back then try the left but try to find a posture that prevents your right shoulder falling forwards and inwards