The common clinical causes of fatigue and drowsiness include long-term sleep deprivation, insufficient blood supply to the brain, and infections. 1. Long-term sleep deprivation: long-term sleep deprivation will make the brain not get normal rest, and the brain cells are prone to ischemia and hypoxia, which clinically manifests as mental depression, slow reaction, memory loss, drowsiness, and so on. 2. Insufficient cerebral blood supply: the elderly, especially cerebrovascular atherosclerosis, can cause cerebral blood vessel narrowing and lead to insufficient cerebral blood supply, insufficient oxygen supply to the brain tissue is also prone to drowsiness, fatigue and other symptoms. 3. Infection: because the body is infected with viruses, bacteria and other pathogens, it is easy to appear body weakness, limb pain, fever, drowsiness and other symptoms, which belongs to the body to fight against the pathogen infection process of the accompanying symptoms. If repeated fatigue and drowsiness occurs, you need to actively consult a doctor and follow the doctor’s instructions for reasonable treatment.