Pulse Ox sleep readings are NOT accurate

Interesting. 

I've never seen my Pulse ox in the 80s yet and I take random measurements 2-3 times a day.

It's mostly always at 96% 

Some early mornings I've seen it at 98 and even 100% after double testing .

this is overnight continuous PulseOx reading during sleep. I've also never seen it in the 80s either during "spot readings". that's why I was initially a bit concerned.

Could you post the graph from the medical grade SpO2 meter? What about the possibility of the watch position changed while you're sleep? What about the possibility of sleep apnea? 

I have had my Fenix SpO2 on "all day" for a week now, varies between 98% to 94%, never drops lower than that and I think that is pretty reasonable and stable.

My Fenix 6x Pro solar also shows from time to time several occurrences of low 80s throughout the night. But maybe that happens, because there was some movement during my sleep while the measurement was in progress? Who knows...

I agree that's why I don't really take much notice of the spot readings but if you check over a week and look at the delta changes I think that gives you much more of an indication of overall trending which can indicate potential issues.

it's already there in one of the 2 images I've posted. the pulse ox is the top one that says SpO2, the rest are related metrics.

that's great then. I think accuracy also varies from person to person due to various factors and the non-ideal location(wrist) for the Pulse Ox measurement.

for me, it's not because of the moments, as I also wear the Oura ring during sleep which is pretty sensitive to movements. On the watch itself, it also has a movement graph during sleep. The low 80s occurrences do not match the high movement periods.
Regardless though, ideally it shouldn't matter as it did not affect the hospital-grade oximeter.

I also have medical grade pulse oximeter at home and the Fenix can be way off, for example when the watch says 92, I get 99 on the Pulse Oximeter. I also get large gaps in the data and for some reason the watch fails to take a reading for hours.

Low SPO2 in the night could indicate sleep apnea, if you can correlate the time of low Spo2 with increased HR and waking up. If you wake up exhausted also. I agree dont freak-out with what's its telling you. You would know if your SPO2 is not right.