Constant yawning is not a disease and most of them suggest that the patient has a lack of oxygen in the brain. It can be clinically caused by a variety of reasons, such as prolonged mental stress, high stress, or lack of sleep. Severe hypertension may cause hypertensive encephalopathy, and hypotension may cause hypoperfusion of the brain, which may lead to insufficient blood supply to the brain, and the patient may suffer from cerebral hypoxia. Patients are also prone to develop diabetes, hyperlipidemia, hyperhomocysteinemia, and cerebral atherosclerosis if they have them. In hyperlipidemia and diabetes, patients generally have increased blood viscosity and slow blood flow; in cerebral atherosclerosis, the lumen is generally relatively narrow. Certain stressful situations may cause ischemia and hypoxia in the brain, and also may be caused by chronic carbon monoxide poisoning.