The reasons for being sleepy after eating a full meal are also divided into the following categories: 1. After a person eats a full meal, blood will be redistributed, and the distribution in the abdominal cavity is significantly increased to absorb the nutrients brought to us by food, resulting in a relative decrease in the effective circulating blood volume, and the effective circulating blood volume in the cranium is obviously reduced. 2. After eating a full meal, in the process of nutrient absorption, there will be a transient mild drop in blood glucose early on, which may also lead to a relative decrease in blood glucose concentration. 3. In the process of nutrient absorption after a full meal, peptides, amino acids and fats will increase the viscosity of blood, leading to an increase in blood viscosity, which may increase the resistance of blood circulation, and may slow down the intracranial circulation.