The main reason for this is that the basal metabolic rate of the human body is very low under the state of sleep, and the blood pressure and heart rate of the human body, including the peripheral muscle tissue, are in a relaxed and resting state under the condition of sleep. The vascular tone is weaker, which leads to poor venous return. Because of the weakened vascular tone, the slow return flow will cause similar symptoms of peripheral bruising, which will gradually recover after the body is awake. But clinically, we should pay attention to the fact that if there is local pressure on one side of the hand alone, we should pay attention to the possibility of poor venous return thrombosis caused by prolonged compression, which is a more critical situation. So if you have unilateral hand swelling, you need to do a venous ultrasound to see if there is thrombosis.