Sudden blackness and fainting may be due to insufficient blood supply to the brain. Insufficient blood supply to the brain is a common manifestation, mostly occurring in middle-aged and elderly people. It can also be easily caused when the body is weak and the blood pressure is low in young people. Patients are also prone to develop it if prolonged massive diarrhea and massive vomiting can cause a drop in blood volume. Inadequate blood supply to the brain includes inadequate blood supply to the cerebellum, brainstem and brain. Patients with insufficient blood supply to the brain may experience blackness in front of the eyes, while patients with insufficient blood supply to the cerebellum and brainstem may experience dizziness, balance disorders and ataxia, which may cause patients to faint in severe cases. In the case of middle-aged and elderly people, most of whom have atherosclerosis, hyperlipidemia and diabetes, the patient’s blood lipids and blood glucose should be monitored. Elevated blood lipids can be treated with oral simvastatin, reserpine or atorvastatin for lipid regulation. Patients with elevated blood glucose are generally preferred to metformin orally, and insulin can also be applied for glucose-lowering therapy if necessary.