I've been on Auto Positive Airway Pressure (APAP) therapy since November 14th, 2011. In the beginning I resigned myself to sleep on my back because I had a full face mask. I gave it a go for a few weeks. Results: Better than my sleep study, but generally not real good. I had an AHI averaging about 5 and a one-day peak at 12 and I started getting a lot of "Central Apneas". Now, real Centrals are a problem, because your brain is not telling your lungs to move, and um, ah, that's kind of important. But in my case I think they were false centrals, more of an artifact of struggling and the ResMed S9 Autoset may score things in its own way. I called the Dr. anyway and they wanted to increase my pressure to resolve the high AHI score. I did, for about 45 minutes. I was over blown and could not tolerate it. What to do? My sleep study said I did better on my stomach, I've always been a tummy sleeper (now I know why) and so I found a way to sleep with a full face mask and switched to my tummy. Wa-La! You can see the big step down in "AHI" in the middle of the chart.
Next, I'm a rather odd duck, I live in multiple places. In the latter part of the above chart, I switched from a home with humidity control and a big bed, to an apartment w/o humidity control and sleep on a smaller bed. Hummm... you can see the difference by eye. What factors are at play here, I'm not sure; humidity, bed comfort, apartment living with a bit more distractions, changes in diet, experimenting with the effects of alcohol, or what?
Just a curiosity is all, and a clue to ponder.