The causes of sudden drop in blood pressure include upright hypotension, acute myocardial infarction, massive pulmonary embolism, etc. The specific treatment should be decided according to the cause of the disease. 1. Upright hypotension: it is mostly seen in elderly patients taking oral antihypertensive drugs. When suddenly changing from lying position to standing position, sudden drop of blood pressure can occur, and even fainting is possible. Immediately after the onset of lying down to rest, elevate the lower limbs, increase the blood supply to the brain, usually pay attention to avoid sudden changes in body position, if necessary, adjust antihypertensive drugs. 2. Acute myocardial infarction: the sudden onset of acute myocardial infarction can lead to a decrease in myocardial contractility, or even malignant arrhythmia, which can lead to a sudden decrease in blood pressure. It is necessary to lie down immediately, ensure a smooth airway, elevate the lower limbs appropriately, and call 120 emergency for help. 3. Large pulmonary embolism: pulmonary embolism can lead to a significant reduction in the left heart blood volume, blood pressure can be suddenly reduced. Patients with pulmonary embolism should also lie down and keep their airways open, go to the hospital immediately for a clear diagnosis, and give thrombolytic therapy if necessary. Sudden drop in blood pressure needs to be highly vigilant, and promptly go to the hospital for treatment.