Don't hold your breath. When you hold your breath, the pressure in the chest suddenly rises, which prevents blood from returning to the heart smoothly and reduces the cardiac output, so the blood supply to the brain is also reduced. Therefore, dizziness is prone to occur, and in severe cases, fainting will occur. When you hold your breath, a large amount of blood suddenly flows back to your heart, which will lead to a sudden increase in cardiac output, an increase in blood pressure, and a sudden increase in blood supply to your brain, which is prone to cerebrovascular accidents.