There are usually three main reasons for yawning all the time: the first reason is that the brain cells are deprived of oxygen, and when the brain cells are deprived of oxygen, they are easily sleepy and tired, so they always yawn. This is due to insufficient oxygen saturation, decreased partial pressure of arterial oxygen, increased partial pressure of carbon dioxide, and often due to chronic pulmonary heart disease, pulmonary hypertension and a series of other reasons that lead to pulmonary insufficiency and cause yawning all the time. The second reason, because of insufficient blood supply to the cerebral vessels, usually related to insufficient blood supply to the vertebrobasilar artery, is that brain cells cannot be supplied with blood sufficiently and effectively, resulting in symptoms of ischemia, which can also cause total yawning. The third reason is that the most common disease that keeps yawning is inadequate blood supply to the heart, which can also cause weakness, drowsiness and yawning when the heart muscle is deprived of blood and oxygen.