Sleep score stark differences for similar metrics?

[JBB1]

I had a sleep score today of 78. Yet I had almost the same metrics as a score a while back at 92 (and with similar results recently). The sleep time, REM and deep sleep were nearly the same. In both cases, the awake time was 10%, with REM, light, and deep exceeding the normal amount for my age (68) - with only 2% less for REM and Deep for the 78 score than the 92 score. I'm not using Premium, which also includes heart rate, so I'm guessing that could be a factor. Any ideas? 

[JohnnyRow]

Sleep score is based on max 50 for time asleep, 25 for deep and REM, 25 for Restoration = sleeping heart rate and movement during sleep/restlessness.

[JBB1]

Ahh, so the metric "Restoration: Sleeping heart rate & restlessness" is missing from the standard subscription. The time asleep, deep sleep and REM were virtually the same for last night's 78 score and the previous 92 score. So the Sleeping heart rate & restlessness must have been very different. Maybe I'll try Premium for one month and see. ...But isn't "restlessness" (I assume that is the same as "movement") what determines deep sleep and REM? I'm confused. How can the movement be both indicative of good deep sleep and REM, yet also of poor "restlessness"? 

[JohnnyRow]

Movement/restlessness is nothing like deep sleep and REM; totally different concepts.

[JBB1]

Aren't REM and Deep sleep determined by movement and heart rate? How are they totally different in determining the metric?

[JohnnyRow]

Maybe I misspoke.  I'm no expert here.

[LZeeW]

@JBB1  According to Fitbit's Help article, Light, REM, and Deep sleep stages are determined from heart rate variability (HRV), not just your heart rate.   For clarification, your Health Metrics report your average HRV, but it is analyzed on a beat to beat basis for sleep stages.

I want to add a personal observation.  I have Premium and my husband doesn't.  Like @JohnnyRow explained, your Deep and REM only account for 25% of your sleep score.  Other factors account for the other 75%, most of your sleep score.  I have to remind my husband of this every time he questions his sleep score.

[JBB1]

Of course, the "time asleep" category is based on the amount of time spent asleep. Meanwhile, Light Sleep, REM, and Deep Sleep are based on movement, heart rate, and HRV.

Sleep time, REM, light sleep, and deep sleep (75% of the score) were nearly identical in duration between the 92 score and the 78 score. So, the part missing in the free app, the heart rate (the last 25% of the overall score) is the missing link. 

I just signed up for a premium trial to see if the heart rate made a difference. It does seem that my heart rate was quite a bit faster than normal last night while I was taking prednisone for allergies. I had just started the prednisone course when I received the mysterious 78 score two nights earlier, so that explains it.  

[kmac56]

I have premium and since the update often have data missing.  This new update has ruined the sleep program