Drowsiness is caused by low blood flow to the brain, elevated blood glucose and increased blood viscosity after a full meal. 1. Low blood flow to the brain: After eating a full meal, the blood will be redistributed, and in order to improve the peristalsis of the stomach and absorption, the blood flow to the gastrointestinal part will be increased, while the blood flow to the brain is reduced, which can easily lead to drowsiness and dizziness due to lack of blood and oxygen. 2. Elevated blood sugar: After eating a full meal, there will be a transient mild increase in blood sugar, resulting in high blood sugar concentration in the blood, causing brain dysfunction, which leads to drowsiness. 3. Blood viscosity increase: after eating a full meal, in the process of nutrient absorption, fat will increase, resulting in increased blood viscosity, thus affecting the blood circulation leading to sleepiness. If you are often sleepy after eating a full meal, it may be caused by other reasons, especially after resting, if you can’t get any relief, you should go to the hospital to find out the cause of the disease.