What is the cause of sleepiness at 9-10 am? The reasons for sleepiness at 9-10 a.m. may be the following: the first is that after breakfast the patient’s blood flows to the digestive system, thus leading to insufficient blood and oxygen supply to the brain, and hence the phenomenon of sleepiness. The second reason is that the sympathetic nerves are more excited in the morning, leading to increased blood pressure and increased blood viscosity, resulting in insufficient blood and oxygen supply to the brain, resulting in sleepiness, so this time is often a factor at high risk of cardiovascular disease. The third factor is to look at the patient may not sleep well at night, the quality of sleep is not high, after a period of excitement in the morning will appear to have a sense of fatigue, so 9-10 am also easy to appear sleepy.