There are two main reasons for arm pain in sleep: 1. It is due to strain or strain in the arm area as a result of strenuous exercise before going to bed, and the inflammation produced can be metabolized in a timely and effective manner due to faster blood circulation during the activity, so it is not easy to have pain. However, when sleeping, blood circulation slows down, leading to the gradual accumulation of local inflammation and the formation of inflammatory edema, resulting in pain in the arm; and because of the cold at night, blood circulation is slower and muscles become more tense, leading to more pronounced pain. 2. This will cause the muscles in the arm to be in a constant state of fatigue, gradually forming strain and inflammatory lesions. After the cold, the inflammation will gradually accumulate, which will stimulate the peripheral nerves and cause pain.