If a patient suddenly stands up and becomes dizzy, the specific causes are as follows: First, the most common cause is upright hypotension, also known as postural hypotension, which is a manifestation of abnormal blood pressure regulation and is especially common in the elderly population. It refers to the clinical symptoms of dizziness, blackness and fainting when the patient stands up quickly after a decrease in arterial elasticity and increased brittleness. Second, for patients who take certain drugs for a long time will also have this adverse reaction, such as long-term use of vasodilators, diuretics, antihypertensive drugs and antidepressants, will have this side effect. Third, various factors lead to insufficient blood volume, such as massive dehydration, or nausea and vomiting after acute gastroenteritis leading to insufficient blood volume, dehydration caused by high heat and heat stroke in summer, bleeding, burns can cause the above symptoms. Fourth, weakened endostatic regulation, such as patients with chronic cardiac insufficiency, long-term bed rest, weakness, and severe anemia, will have this symptom.