The survival time of cancer patients after they appear drowsy all day is related to the type of disease, individual condition and care, and the exact survival time cannot be generalized. The drowsiness of cancer patients is mainly related to the spread of cancer cells to the brain, metabolic disorders and infections. The spread of cancer cells to the brain in the late stage of cancer destroys the corresponding nerve cells and competitively accelerates the consumption of blood oxygen, causing irreversible damage to nerve cells and resulting in impaired consciousness. The greater frequency of drowsiness in advanced cancer suggests a higher risk of death in a short period of time, but the exact survival time cannot be determined. In contrast, drowsiness caused by metabolic disorders can be adjusted. For example, drowsiness caused by high blood ammonia level due to liver cancer can be reduced by medication or dialysis to reduce the blood ammonia concentration and prolong life expectancy. It is recommended that cancer patients who experience drowsiness should pay particular attention to the frequency of occurrence and contact their primary care physicians as soon as possible to clarify the cause of the disease and then take appropriate treatment plans.