Male, 29, smoker, not overweight, experiencing left shoulder/arm pain at night while sleeping, cant sleep because of it, no pain during the day.

Shoulder pain: Possibilities include tendonitis of shoulder, torn rotator cuff and a bulging disk in the neck vertebra. Your symptoms appear positional. I would expect the shoulder pathology would also be noticeable during the day and with shoulder motions. Consult an orthopedic specialist. If no shoulder pathology is found, referral to a neurologist may be made.