Sleep score has changed for the worse since iOS upgrade

My initial reaction to your post was to write: "You're Dreaming".

...but that is obviously the reverse of what is being reported.

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There was notification is the upgrade for iOS 26.2 that suggested sleep scoring had changed.

But detecting less REM sleep has not been reported here.

It is not likely to be a software error -- you may in fact be dreaming less these last few nights. By fiddling with the Health app on your phone, you can compare current to Average REM amounts over time, weekly, monthly, or 6 month-ly.

I've had a similar trend in my sleep tracking since the upgrade to 26.2, my sleep tracking has devolved to "No Data" since the upgrade. I've upgraded, rebooted, unpaired, re-paired, still "No Data". I've talked with tech (can't remember what level) before recently, and she had no answers to the "No Data" problem. It's possible that my sleep has actually deteriorated to the point of "No Data", but wouldn't the watch track a low score...even "0" rather than "No Data "? "No Data" implies to me that the watch is not tracking. What do you think?

Did you also update WatchOS to 26.2?

I find watch upgrades difficult because it requires the Watch be on the charger and charged at least 40 percent AND the phone be nearby the whole time.