Heh, I can speak to this. Of all the coincidences, I'm currently undergoing nerve conduction studies for the radial nerve damage mentioned above and have had countless conversations about both ulnar and radial nerve compression with a physio, a radiologist, a neurologist and now a sports physician.
You're correct re ulnar nerve, but occasional numbness isn't generally something to worry about. It can be caused by something as simple as sleeping with your arm above your head for part of the night. If it's combined with pain, muscle weakening or clicking of the elbow, then it's something to get checked out.