Waking up in the middle of the night with a heartbeat of 80 and then 65 after a while is due to fluctuations in heart rate. Heart rate is the number of times a normal person’s heart beats per minute in a quiet state, and a normal person’s heart rate is 60 to 100 beats per minute. The heart rate is affected by a variety of factors, such as nerves, body fluids, self-regulation, etc. to adapt to changes in the body to maintain stable blood pressure. Sympathetic excitation causes the heart rate to speed up, and parasympathetic excitation causes the heart rate to slow down. When the parasympathetic nerves are in an excited state during rest and sleep, the heart rate is generally slower. When the sympathetic nerves are in an excited state in the morning and during exercise, the heart rate is generally faster. In the middle of the night, when the sympathetic nerves are excited, the heart rate is faster, and after a while when it is quiet, the parasympathetic nervous system dominates and the heart rate slows down, which are all normal heart rate fluctuations. If you experience frequent panic attacks, it is advisable to go to the hospital to check for arrhythmia.