Seems like neuralgia or poor circulation due to bad posturing while sleeping may cause such pain. Your muscles seems to have lost strength and have become soft and lax. You need exercise of left arm and also consult for better understanding and treatment.

Hello, I understand your pain. Chest pain may be of various reasons. But we cannot take it lightly what ever It is it should be sorted out by the means of investigation but before that it may also be diagnosed clincally. So just meet a local general physician so that he may examine you and may come to diagnose your condition or may investigate you for the proper treatment. Thank you