Hi Kim @kim555, Welcome to Connect. I have idiopathic small fiber peripheral neuropathy along with PMR and a few other conditions including carpal tunnel syndrome. Because I'm a side sleeper, I too have had many nights in the past where my hand and arm go to sleep and I wake up in pain. What has been helping me is being more careful about how I hold my arm at night so that I don't lay on it which I think makes it worse for me. I've found that using a smaller travel pillow on top of a regular pillow allows me to have my arm on top of or under the larger pillow so that I don't lay on it.

I think the numbness for me is more nerve related than anything to do with PMR since my PMR is currently in remission but hopefully you will get some answers when you see your rheumatologist. I thought you might find the following article from the Sleep Foundation helpful.
-- Numbness in Hands While Sleeping: Why It Happens and What It Means
https://www.sleepfoundation.org/physical-health/numbness-in-hands-while-sleeping.
Can you let me know what you find out at your appointment with the rheumatologist?