1. Heart rate 48 is normal after sleeping, because the metabolism of the body is lowered and the vagus nerve is excited when sleeping, so the heart rate will decrease. 2. Heart rate refers to the number of heartbeats per minute in a normal person in a quiet state, generally 60 to 100 beats per minute, there are individual differences, athletes’ heart rate than normal people will be a little lower, at about 50 beats per minute. 3. When an individual is asleep at night, his or her metabolism slows down and the vagus nerve excitability increases, all of which can lead to a slower heart rate. 4. At the same time, certain medications and certain diseases can also cause the heart rate to slow down. If accompanied by other symptoms such as wheezing after activity, chest tightness and other symptoms or self-consciousness, it is recommended to go to the hospital for cardiac examination.