Upper left arm pain at night ...

So recently when I’m sleeping I will get sever pain in my upper left arm. To the point I can’t breath or move almost as if I’m paralyzed on my left side( For a couple seconds). It only happens when I first wake up. I am a left side sleeper. So I thought at first I was maybe just sleeping the wrong way, but the pain has become unbearable and happens every night. Idk how to fix it or really what is wrong with me. I know it isn’t a heart attack because it has been happening for a couple weeks. Im also only 21 and healthy.