Is it normal to have bradycardia while sleeping?

Sleep physiology: During sleep the body's physiology changes, and it does so per stage of sleep, so there can be times that the heart is slower, however, it can also slow down due to illness - for example in untreated sleep apnea the low oxygen levels can cause bradycardia, or low oxygen levels from emphysema.

Bradycardia : It is normal to have slower heart rate with bradycardia during sleep , obviously the degree of slowing is important to say whether it is normal or not