Happens to me almost every night, it's been happening for years

I used to get it every night...got a good mattress with a pillow top...never got it again,

Its absolutely a nerve compression someplace can be severral places but from the shoulder down its likely in your upper spine.

get a good mattress dude....

I think that is called a charlie horse, if it is then start drinking more water and getting potasium in your system (bananas). I used to get them a lot and it was because of the lack of water and potasium in my system.

happend to me twice recently, very annoying

Well, slept on the couch and it didn't happen. Looks like its time for a softer matress!