There is no fixed which three diseases of old sleepiness. Drowsiness may be a normal physiological phenomenon, or it may be a disease, such as arteriosclerosis, hypothyroidism, obstructive sleep apnea and so on. 1. Physiological phenomenon: Insufficient sleep, overwork, etc. will be prone to sleepiness, which is a normal physiological phenomenon. 2.Diseases (1) Atherosclerosis: These two diseases will affect the speed of blood flow, resulting in insufficient blood supply to the brain, and the lack of oxygen and blood to the brain will cause fatigue, drowsiness, and sleepiness. (2) Hypothyroidism: insufficient thyroid hormones will lead to reduced metabolic rate and sympathetic excitability, which will cause unresponsiveness and, in severe cases, mucous edema, causing drowsiness. (3) Obstructive sleep apnea: narrowing of the upper airway or decreased ability to maintain open function will lead to sleep apnea or hypoventilation, which will seriously affect sleep quality, and even short-term hypoxia, and symptoms such as daytime sleepiness and drowsiness. Need to pay attention to the old sleepiness is not necessarily just three diseases, should go to the hospital in time to identify the cause of the disease for treatment, do not delay the condition.