Rapid heartbeat when lying down may be caused by physiological or pathological factors, such as cardiac arrhythmia, cardiac neurosis and so on. 1. Physiological factors: If there is excessive mental stimulation before going to bed, such as high tension or drinking strong tea, alcohol, coffee and other stimulating beverages, it will cause sympathetic excitation, and the heart beats faster when lying down. 2. Pathological factors: (1) Cardiac neurosis: when experiencing mental stimulation and excessive nervousness, it leads to disorders in the excitation and inhibition process of the cerebral cortex and autonomic dysfunction, which may lead to rapid heartbeat when lying down. (2) Cardiac arrhythmia: If high blood pressure or aortic stenosis causes left ventricular overload leading to left heart failure, cardiac arrhythmia may occur, and the heart may feel faster when lying down, accompanied by dyspnea. When a rapid heartbeat occurs, it is recommended to consult a doctor in time, follow the doctor’s instructions for further examination, clarify the cause with the help of the doctor, and carry out targeted treatment or therapy.