HRV varies during sleep and from minute to minute due to a variety of factors, including the body’s natural rhythms and responses to various stimuli. One factor that can affect HRV during sleep is the activity of the autonomic nervous system (ANS). The ANS controls functions such as heart rate, blood pressure and digestion, and its activity can vary depending on the stage of sleep a person is in. For example, HRV tends to be higher during rapid eye movement (REM) sleep, which is associated with increased ANS activity. You can also click o the info button near the HRV graph to read about it.

My HRV recently varied from 10 to 130 when I was sleeping. It got lower when I was taking slow deep breathes.