Sitting and sleeping with a fast heartbeat may be an arrhythmia attack, it may also be uncomfortable to sleep in a sitting position, resulting in poor sleep caused by sympathetic nerve excitation. 1. Sitting and sleeping, if there is a fast heartbeat may be an arrhythmia attack, such as atrial tachycardia, sinus tachycardia, supraventricular tachycardia, etc., to be clear if you need to do an electrocardiogram. 2. There is also a situation may be sitting for sleeping uncomfortable caused by normal people are lying down position to sleep, in the sitting position to sleep may not be accustomed to, poor quality of sleep, sympathetic excitation, resulting in rapid heartbeat, this case adjust the sleep position should be able to relieve. In this case, adjusting the sleeping position should be able to alleviate the fast heartbeat. If you want to clarify the cause of the fast heartbeat, it is recommended that you go to the hospital for consultation.