Why do my arms go numb while i am sleeping on my side?

Many possible causes: Chances are your are sleeping in a position that is impinging on the blood supply to nerves, kind of like when your legs fall asleep while reading a good book on the toilet:). If there are any other symptoms that go along with this then see a neurologist for further work up. There are a lot of neurologic conditions that can cause this as well. Consult with a neurologist as you see fit.