Possible reasons for elevated blood pressure after sleeping at night include autonomic dysfunction, disease effects, postural hypotension and so on. 1. Autonomic dysfunction: Normally, sympathetic excitation dominates during the daytime and blood pressure is high; vagal excitation dominates at night and blood pressure is low. If the autonomic nerves (i.e. sympathetic and vagus nerves) are dysfunctional, it will easily lead to higher blood pressure at night. 2. Disease effects: for example, patients with sleep apnea syndrome are prone to hypoxia during sleep at night, which will increase the blood pressure due to the stressful state of the body. 3. Postural hypotension: blood pressure is high when lying down and low when standing up, which can be caused by lying down at night. In addition, the combination of heart, kidney, brain damage or high blood pressure caused by other diseases, the so-called secondary hypertension, etc. may also appear after sleeping at night the phenomenon of elevated blood pressure. The pattern of high blood pressure during the day and low blood pressure during the night is important for maintaining the normal structure and function of the cardiovascular system. Therefore, people with elevated blood pressure at night are at increased risk for later cardiovascular complications, such as enlarged left ventricular hypertrophy, stroke, and kidney damage. Therefore, people with elevated blood pressure at night should go to the hospital in time for treatment.