Whine, whine... grow up already.

You said "for years", but how many please? What are the run hours on it?

And post it here - we'll help interpret and suggest adjustments if necessary.

But even if you have jagged edges, if you take them with water, the edges become negligible.

You may find you get quite a few (more) hypopneas than usual as well though your machine may compensate for them of course.

Can you post new Oscar data? Sounds like your neuro. has a brain!

And that answers the OP's original question how?

Maybe you could look into other reasons for your stiff neck like sports etc. on similar days...

Cervical collars work for those who need them - for when their head drops down and cuts off their airway, probably more often in side sleepers, but not always. If you didn't have that problem, why did you try the collar? And if you did have it, then other adjustments may need to be made with or with...

Sleeping on your back, side, ???

I would want my GP to refer me to another hematologist, not a sleep doctor, as OSA may be blamed for some other not yet diagnosed problem, and the apnea may only be secondary issue.

...

It's important to get the pressure graph in there - yours is sort of stuck at the bottom, not really visible...

Do you want to make bets re who'll die first - the bacteria or you?

SC is garbage and you don't want ozone fumes in your lungs! Google the residue from their filters and see if you get any hits.