Sudden syncope is mostly caused by some diseases, such as reflex syncope, cardiogenic syncope, upright syncope and so on. 1. Reflex syncope: it is considered to be caused by cardiac depression due to vasovagal reflex and systemic vasodilatation, resulting in reduced cardiovascular flow and cerebral ischemia and hypoxia, which in turn causes sudden syncope. 2. Cardiogenic syncope: this situation may also be due to a sudden decrease in cardiac output, which caused sudden syncope. It is mostly seen in cardiac arrhythmia, such as atrioventricular block, cardiac output disorder, acute pericardial tamponade and so on. 3. Upright syncope: sudden syncope can also be considered as a result of changes in body position, blood pressure regulation disorder. Sudden syncope is caused by many reasons, it is recommended not to diagnose yourself according to the symptoms, you should go to the regular hospital in time to clarify the cause of the disease, and follow the doctor’s instructions to standardize the treatment.