I had already tried increasing my pressures slightly and I didn't want to play around with that anymore until I've seen the sleep doc, but AshSF suggested switching on the EPR on my Resmed s9 Auto, which I'd previously not been using. I tried one night on the lowest setting, and lo and behold, the hypopneas dropped! I kept the EPR the same for a couple of nights to make sure it wasn't a fluke, and I've now cranked the EPR up to 2. They dropped again! In just over a week, the hypopneas have reduced from an average 38 per night, to just 7. Hallelujah!!
I know this is mystifying. Many people on here have said that EPR actually INCREASED their hypopneas, but I guess everyone is different. I will keep monitoring things and talk to the sleep Doc but I'm hoping I've cracked it this time. AHI is now hovering around 3, which I think can improve, but finally it's heading in the right direction, and critically, I am starting to FEEL a lot better. Thanks everyone for all your input.