After a meal, food will reach the stomach and be digested and absorbed. Since the stomach requires more blood flow for digestion, blood is supplied to the digestive tract first as much as possible, so there is relatively less blood flow to the brain. However, since the brain is more sensitive to oxygen or sugar, once blood flow is reduced there will be less oxygen, so you may feel sleepy. Since food is present in the stomach, more blood flow is absorbed during digestion and absorption peristalsis, so rest may be appropriate for better digestion and absorption. When food reaches the duodenum or ileum or small intestine, gastric blood flow will drop, and at this time the blood supply to the brain becomes more, so the symptoms of drowsiness will be relieved. In summary, after eating a large amount of blood flow needs to pass through the gastrointestinal system, in order to help digestion and absorption of food, so there may be sleepiness or a significant lack of blood supply to the brain. At this time, you can take a short rest and wait for the symptoms to be relieved after the food is digested.