There are three main reasons for the pain in the arm when you get up from sleep: 1. During the day, the strain on the arm can occur due to more intense activity or longer muscle pulling time and greater force in the arm position. This kind of minor strain, when the blood circulation is better, such as more activity during the day, blood circulation accelerates, it will lead to the formation of some local inflammatory metabolites gradually metabolized, there will be no accumulation, so there will be no obvious pain; and the initial edema of the injury is a little lighter. After sleeping at night, the edema will gradually increase during the night and blood circulation will slow down at night, which will lead to the accumulation of local inflammatory metabolites, so you will feel obvious pain when you sleep. 2, during the night sleep, the arm is not fully relaxed or side lying arm pressure, which will lead to muscle tension in a relatively long time. The arm will feel painful after sleeping. 3, due to cold, cold during the night sleep will lead to slow blood circulation and muscle tension, so it will also lead to the accumulation of inflammatory metabolites and arm pain.