High blood pressure suddenly low, if lower than 90/60mmHg, or than the usual basal blood pressure systolic blood pressure drop of more than 30mmHg, consider the possibility of shock. Common causes are as follows: 1, postprandial hypotension, especially common in the elderly, after eating a large amount of blood running to the stomach, digestive tract, peripheral blood supply is less, the blood pressure measurement site blood is also less, the amount of blood pressure will be low; 2, postural hypotension, the elderly lying down blood pressure is normal, one station up pressure receptor regulation function is reduced, blood pressure will also appear suddenly drop, resulting in dizziness and even angina attack; 3, heart disease For example, heart attack, widespread anterior wall infarction blood pressure drop; 4, pneumothorax, chest tension will also affect the blood pressure drop; pericardial tamponade will also cause a drop in blood pressure; 5, with short-acting antihypertensive drugs such as nitroglycerin, captopril, lowering blood pressure very quickly, especially nitroglycerin within five minutes blood pressure can drop 40mmHg, so the application of antihypertensive drugs need to follow the doctor’s advice and pay attention to monitoring.