This SAME thing is happening to me and three doctors are completely perplexed by it.

One doc had said it sounded like degenerative disc disease of the back ... when you're sleeping, your body is in one position for a long period of time, which is why in theory it'd happen more at night than during the day because of a nerve being pinched. But my X-rays and MRIs come back normal with no abnormalities.

I have always slept on my right side, and now I can't even sleep on the left because my right arm will go numb then, too. Sometimes even happens when I'm on my back.

This is really, really disturbing to me because I'm not getting any sleep. It's extremely difficult for me to fall asleep these days.

For me it's not just the hand (which can indicate carpal tunnel) but the entire arm from shoulder to fingertips. It can be either arm, but it's primarily my right.

It also has happened to my legs, but not recently.

Only happens at night.

I still have no explanation. Have not had an MRI of my head but I don't have headaches or dizziness or anything like that.