Hi cpappi,
The amount of REM during a sleep study can be reduced by the "First Night Effect."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2925054/
With mild OSA there is a small possibility that a CPAP may help you but in most cases it will not.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4163952/
They conclude:
"Individuals with mild OSA in this cohort do not have worse sleepiness, mood or quality of life in comparison to those without OSA."
There is a possibility that CPAP could make your sleep worse, especially if you have mild OSA with a low arousal threshold.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5940420/
From this study:
"PAP may not fix their sleep-related respiratory disturbances, and conceivably, could make them worse."
I agree that you should start treating your mild OSA, but CPAP might not be the best course of action.
On Resmed's site they do not recommend starting with CPAP for mild sleep apnea.
Measuring the outside of a neck is much easier than measuring the inside(throat). There is a very strong correlation between neck size and OSA severity. That is why it is used.
Tongue/throat exercises have been shown to reduce the size of the neck as well as reduce your OSA.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4402674/
They conclude"
"Current literature demonstrates that myofunctional therapy decreases apnea-hypopnea index by approximately 50% in adults and 62% in children. Lowest oxygen saturations, snoring, and sleepiness outcomes improve in adults. Myofunctional therapy could serve as an adjunct to other obstructive sleep apnea treatments."
There are several ways to reduce your OSA without using a CPAP. These methods typically work best for young people with mild OSA.
CPAP works best for people with moderate to severe OSA. Most of the people on this site have severe OSA that has been helped with CPAP. They will push CPAP even when there is a lot of evidence that it will not help someone with mild OSA. There is a current thread "Feeling worse on CPAP" that you might want to read. The poster that started the thread has mild OSA, (an AHI of 11)...
Cue the CPAP shills.
Using weight loss, general exercise, and tongue/throat exercises I managed to get my AHI down to approx 5.
Not using a machine currently.