Thanks for you comments. I'll try downloading the program you suggested and looking at the data. I agree that assessing the level of sleepiness is subjective. But the reduction in the level was pretty dramatic and I repeated the experiment by increasing the pressure on my CPAP until I felt significant daytime sleepiness again. It could just be a coincidence but at this point I'm thinking its not.
A little background. I have been using a cpap for maybe 7 years now. I have always had "residual sleepyness" despite using my cpap more than 90% of the time. I should also add that I tolerate my cpap well and it causes me little or no discomfort. I had a sleep study done and it suggests I have severe sleep apnea. I have a ResMed sleep apnea device.
Recently I noticed that I had far less day time sleepyness when I didn't use my machine for several days. My pressure was set between 10 and 15. I thought this was ok because my AHI score was typically around 0.5. I complained that I still had daytime sleepyness but my doctor concluded that my cpap treatment was working effectively after downloading the data.
To test what my baseline AHI score was i decided to put the machine on its lowest pressure setting of 4. This is below what should be helping me. I still had a AHI score of about 0.5, which is I believe very good. I've tried slowly turning my cpap pressure back up and long story short my AHI score seems to be independent of my pressure setting ie its always about 0.5. I also started to feel sleepy durning the day again once my max pressure got above 8.0 or so.
I also have a Fitbit. The Fitbit suggests that my sleep quality is about the same no matter if I use the CPAP or not ie i get plenty of Deep/REM sleep and O2 variations seem low.
Anyone know what could be going on? Is it just time to get a new sleep study done?