What you need to know about Heart Rate Variability (HRV) data collected during the night

As more devices are able to collect high-quality Heart Rate Variability (HRV) data during the night, a few questions come up:

• What data should we use as HRV score? The average of the full night? Or maybe data collected during deep sleep or a specific deep sleep segment? What factors should we consider when making this call? (circadian rhythm, the accuracy of sleep stage detection..)
• What are the differences between night and morning HRV measurements, and under which circumstances one might be preferable to the other?

In this post, I will try to answer these questions and show data that should clarify a few important aspects. In the process, we’ll have to debunk some common misconceptions.