Human sleep can be divided into two different stages, non-REM sleep and REM sleep. During REM sleep is when most dreaming occurs. And while we dream, our brain temporarily paralyzes our muscles to minimize potential harm that would occur if we acted out the dreams we had. However, when the throat muscles get paralyzed in REM sleep, the throat becomes even more floppy, and obstructive sleep apnea (OSA) can be more severe. In some patients, the difference in OSA severity from NREM to REM is quite striking - some patients have OSA confined almost exclusively to those periods of REM sleep.
Some sleep researchers feel that OSA confined only to REM sleep may not be as serious as OSA that is present in both stages of sleep, as I have blogged about before. But in my experience, patients that treat their REM sleep-related OSA often have an improved quality of life.
This article showed that the more severe the OSA is in REM sleep, the worse control of diabetes. It's not clear why that would be, but the findings do not support the thinking that REM sleep OSA is less serious. The study authors point out that since most REM sleep occurs in the second half of the night, patients who don't use their CPAP all night may be at greater risk of having less control of their blood sugars.