Fast heartbeat when lying down may be present with excessive anxiety, hyperthyroidism, cardiac insufficiency and so on. 1. Excessive anxiety: Some people may have excessive anxiety and mental stress, which may lead to rapid heartbeat and palpitations when lying down. 2. Hyperthyroidism: the level of thyroid hormone in the patient’s body will increase, resulting in a faster heart rate, and the symptoms may become more obvious when lying down. 3. Cardiac insufficiency: patients may have organic heart disease, serious heart disease will appear cardiac insufficiency, lying down due to the increase in the amount of return blood, resulting in increased cardiac load, can be a reflex to accelerate the heart rate, and serious can also be accompanied by dyspnea. If the symptoms are obvious, you should go to the hospital in time, make a clear diagnosis under the guidance of the physician, and give targeted treatment.