Charge 2, HRV, and REM + Deep Sleep Stages

[topannuity]

I've been wearing a Charge 2 for about a year and diligently recording my sleep stage data in an Excel file when I wake up. Recently, I also purchased a Corsense HRV sensor and began measuring my morning HRV (Heart Rate Variability) level using the EliteHRV app. I enter this data into my Fitbit Excel file, too.

Below is a graph showing the Fitbit time in REM added to time in Deep Sleep (purple dotted line) in comparison to the HRV data (red solid line). In order to remove spikes in the daily data (which occur every few days), I've "normalized" all the numbers into 7-day moving averages.

The reason for this posting is that I've discovered an anomaly which I am unable to explain and would like to get feedback from the community.

Apparently, there is an INVERSE relationship between Fitbit's reported time in REM+Deep sleep versus my morning HRV measurement. You can see in the graph the two are moving in opposite directions most of the time.

I googled HRV and could not find any reason or explanation for this inverse relationship. If anything, the literature expects the opposite result, which is, that following a night when I spent a lot of time in REM+Deep sleep stage, my HRV values the next morning should likewise be HIGHER. And conversely true too.

The Excel data shows the opposite. Does anyone have an explanation why this may be happening?  (And, no, I didn't reverse the data on the graph. The phenomenon I'm reporting is correct, just without a logical explanation I can think up.)

[AlvaroFitbit]

@topannuity, welcome! It's good that the community is growing! 

Thank you for sharing your data about sleep recorded by your Charge 2. Since the data is analyzed by Fitbit's algorithm and they are proprietary information I wouldn't know how the data from a different device may be opposite to what you see on your Fitbit account. Still you can try having a sleep test done if you wish to better understand your sleep behavior. For this you will need to consult your health specialist.

Let me know how it goes.