The hazards of sleeping during the day and working at night. First, a long time will affect the body’s hormone secretion, especially the secretion of melatonin, melatonin is mostly secreted at night, sleep during the day due to the brighter sunlight, almost or rarely secrete melatonin. Melatonin can play the role of sedation and sleep, help people sleep, can enter the state of deep sleep. For the daytime is difficult to enter deep sleep, a long time will affect the quality of human sleep, and in serious cases will appear sleep disorders of the disease. Secondly, sleep during the day and work at night, due to the night time when the vagus nerve excitement, if a long period of time sleep during the day and work at night, can also appear during the day time to induce the vagus nerve, also will appear excited. Long time the vagus nerve is in an excited state, may induce heart diseases, such as premature heartbeat or angina pectoris, and in serious cases, myocardial ischemia. For this condition, which is even more harmful to middle-aged and elderly people, patients are advised to work intermittently at night if necessary.