The causes of sudden fainting for a second without any signs are considered as follows: First, it may be caused by transient cerebral ischemic attack, if the patient has severe stenosis of cerebral arteries, it is easy to have fainting for a second without any signs. Especially when the weather changes, it is more likely to appear. It is recommended that the patient improve the head vascular examination or head CT examination in time to clarify. The second aspect is that the asymptomatic dizziness may also be caused by postural hypotension, which is a characteristic attack of the disease and usually occurs suddenly during the patient’s squatting and getting up, accompanied by blackness in front of the eyes. The third aspect is that a sudden, unsuspected fainting spell may be caused by otoliths if it is related to a change in the position of the head.