Frequent yawning and sleepiness are caused by the following factors: 1. The most common factor is the lack of oxygen. 2. cerebrovascular insufficiency of blood supply, such as cerebrovascular ischemia, or a history of stroke, may also occur due to cerebrovascular insufficiency of blood supply and yawning, sleepiness. 3. hyperlipidemia, such as high cholesterol or high triglycerides in blood lipids, may also occur due to thick blood lipids, yawning, sleepiness.