In MOST cases it actually is a structural issue. The brain anomaly that causes paused and intermittent breathing is much more rare.

Sure, and I wouldn’t tell someone to not see an ENT, and maybe a CPAP, surgery, or this pill are the right solution for you. I’m just throwing out another option to consider with different tradeoffs.

fwiw I really believe it is, my sleep problems come and go based on entirely physical variables--how flexible I feel, how much time I spent "shrimping", how tight my back and neck are.

Personally I would not be surprised at all if in 50-100 years we look back on this era as one where we massively overprescribed CPAP machines to treat an entirely-fixable condition in most people (alongside all the other medical interventions that will turn out to be bandaid fixes for actually fixable problems). I'm aware this is a bit of an outlandish take. But you can tell how many people's breathing and posture is bad just by existing in the world for ten minutes and looking at them. I think it's really an epidemic.