Fainting after urination may be caused by blood pressure drop caused by holding urine, arrhythmia related, ectopic pheochromocytoma and so on. 1. Decrease in blood pressure caused by holding urine: when patients hold urine for a long time, the blood circulation in the body increases, and when they urinate, the blood circulation decreases rapidly, leading to a decrease in blood pressure and cerebral ischemia, so they feel dizzy. 2. Cardiac arrhythmia: If A.S. syndrome occurs, the patient’s heart ejection volume decreases, and the brain also decreases the blood volume, and when it is more serious, it is possible to faint. 3. Ectopic pheochromocytoma: belonging to adrenal gland tumor, ectopic pheochromocytoma will produce catecholamine substances, making the patient hypertensive, and fainting in severe cases. If the phenomenon of fainting after urination may also be other reasons, you should go to the hospital for consultation and examination, so that professional doctors can help treat the disease to avoid delay.