The constant sleepiness and lack of energy is considered to be due to inadequate blood supply to the cerebral arteries due to various reasons. For example, poor heart function, low blood pressure, failure to reach the blood flow pressure supplying the cerebral arteries, or too little oxygen provided by the blood per unit volume due to anemia, or due to cerebral arteriosclerosis, can lead to insufficient blood supply to the brain. When brain cell metabolism is affected, it is easy to become sleepy and unrefreshed, which can manifest as yawning. You can see a doctor for a cerebral blood flow test to find the cause and give timely treatment.