I think positional apnea is only a problem for mouth breathers.

[BoxcarPete]

Mouth breather here, severe clustering in REM, especially on my back. Chin tuck test cuts off flow completely for nasal inspiration only. I can breathe out through my nose or both directions through my mouth.

I get serious clusters in REM on my back, even with CPAP. A collar "upgrades" those to RERA and Hypopnea, if I can stay on my side CPAP seems to make them go away. Still struggling to find a way to make that happen reliably at a pressure that doesn't get me exhaling through my stomach!

[Nightynite]

BoxcarcarPete, Thanks for the reply. I was also a mouth breather for 55+ yrs. Decided to see if I could make the change. After a few weeks and a little tape I retrained my brain to only breathe through my nose. It’s a worthwhile challenge that’s achievable for a person with the right mindset.

[Gideon]

Read the footnote in the cervical collar wiki for medical references