Are your Spo2 records good at night?

I looked at mine , The graph is always between 90 and 100 . Is your watch tight. Mine is tight on my arm.

What pose do you sleep in? Are your arms under your body? Bent elbow? You have to understand that spo2 is measured on your hand and if blood circulation in your arm is bad, you will get exactly the values you have.
Good sign though, is when you get up, your score goes back to 99-100%. You are alive again, bro ;)

The accuracy of SPO2 readings on watches in general is rather unreliable. It should not be used for important medical purposes. 
I did however get a low reading from a professional instrument at my doctor. Both me and the doctor was surprised about the value, so I did a reading with my watch. It was well within the normal range, so the doctor went to find another instrument, which happened to agree with my watch. 

Little up. Can some share their night spo2 plz? Still having up and down. 

I tried it for a few nights and have graphs kind of like yours but they are mostly in the 90-100% range and only dip to 85% a couple times.

In this "Sleep" chart I toggled on the respiration rate and it did not seem to have any sudden changes where there were dips, so I suspect it was arm posture affecting the measurement.

I decided that together the measurements tell me I probably don't have any sleep apnea issues. So I stopped using the function again.

Here's mine from today:

This is pretty typical for me - a total score of low 90s, and some dips to 80%.

I chose to not worry about it too much, because I think it's just inaccuracies of the sensor.
I never had spo2 on during the day, I'll turn it on now and see how that looks.

I have it mostly turned off, not sure why I enabled it yesterday ;)
My girlfriend has a Venu 2, which I believe has the same sensor, and snores (I hope she doesn't read this forum, because she would kill me if she knew I told anyone). Her nightly readings are better than mine

My nightly average never drops below 92%, usually it's in range 94-96%. I think it depends on the body/hand position during sleep, because when I do occasional checks during the day, it's always 96-98%.

If yours is around 90% or so and is stable in time (during weeks and months), I wouldn't worry about that. I can't imagine the sensor could work perfectly for all hands in the world. 

Edit: Of course there are single drops down to ~80% during the night, but I think they are rather results of unfavorable hand position, not breathing problem - at least in my case.