There are many reasons for sudden blackness and fainting, including hypoglycemia, malnutrition, anemia, transient cerebral hypoperfusion, and pernicious arrhythmias. Darkness before the eyes and fainting may be due to transient cerebral blood perfusion deficiency with complex causes. If syncope occurs occasionally, it can be temporarily observed to avoid triggering factors. If frequent syncope occurs, active hospital consultation is required to clarify the cause of syncope and provide targeted treatment. Insufficient blood supply to the brain occurs mostly in middle-aged and elderly people, and is related to atherosclerosis, hyperlipidemia and diabetes. At the same time, young people with weak constitution, low blood pressure, chronic diarrhea, vomiting, and strenuous activities can cause a decrease in blood volume. In addition, emotional stress and anger can also induce arrhythmia and transient ischemic attack. Patients can go to the hospital for blood pressure, blood sugar, blood routine, electrocardiogram, cardiac ultrasound and other examinations to clarify the cause of syncope so that timely treatment can be carried out.