Severe left arm pain at night time unable to sleep wih pain, no pain during the day.

Evaluation. Can be anything from a pinched nerve to a rotator cuff problem in the shoulder to nerve compression under the armpit. Needs evaluation.
This is tissue pain. Without knowing the site or quality of the pain, consider mild inflammation of the soft tissues or of the joint capsule. If you sleep with your arms over our head, you could be putting traction on the nerves to your arm; if your neck is over extended or fully flexed the cause of the pain could be in your neck warning to see your doctor so that the problem doesn't get worse..