I damaged my ulnar nerve some years ago (due to an argument with a cycle barrier in a dark alley - which I lost). For some time I had little feeling in my 3rd and 4th fingers of my left hand. I wasn't playing much at the time anyway, so it didn't really affect me much from that point of view, but I do remember it was extremely painful whenever I accidently knocked my "funny bone". In the end I was advised to have surgery to move the nerve - which I did. I still have a slight numbness on the left side of my little finger, but it doesn't affect my playing at all.
Surgery is probably a bit extreme for your case though - so I'm not sure what to suggest other than trying to avoid sleeping in positions that cause the problem - but I'd guess you do that anyway.
James Lister, luthier, Sheffield UK