Below is an instruction that describes a task. Write a response that appropriately completes the request. ### Instruction: Is brain fog/cognitive dysfunction in sleep apnea caused by sleep fragmentation or intermittent drops in SpO2?24M, 176cm, 78kg, mild sleep apnea (AHI = 10), not on any meds, non-drinker, non-smoker.I have had mild OSA for the last 2 years and was only recently diagnosed in March; during this time, my main symptom is brain fog/cognitive dysfunction which was bad enough to impede my ability to study. I have since been treated with CPAP and I have noticed mild improvement even though I am still not 100% used to the machine and the mask and am hence sleeping only for 6 hours at a time. I still feel sleepy on days where I sleep this little, but the brain fog is improving gradually nonetheless. This makes me wonder: was the brain fog caused by the oxygen deprivation while my OSA was untreated, or was it due to the sleep deprivation? If it was caused by sleep deprivation which occurs as a consequence of the OSA, then why am I experiencing improvement in the brain fog even though I am feeling sleepier than most of the days before I began using CPAP?. ### Response: They are both tied in together, as the low oxygen level triggers an awakening response that fixes the low oxygen level but results in sleep fragmentation. Disorders that are associated with frequent awakening but not hypoxia, such as restless leg syndrome, are also associated with "brain fog" and other symptoms of poor quality sleep so it isn't really just the oxygen.There are two possibilities here for you.Cognitive dysfunction and daytime sleepiness are not affected equally by quantity/quality of sleep though they are related. It is possible that 6 hours of higher quality sleep is helpful for your cognitive symptoms, but isn't enough to pay off the sleep debt you've accrued especially since total sleep has decreased. Increasing comfort over time with the CPAP is the rule of thumb, and eventually it tends to become a sleep cue.The other possibility is your cognitive improvement is a placebo effect. Your OSA is mild by AHI, depending on the rest of the picture including nadir oxygen and other symptoms (snoring, high blood pressure etc) this may or may not be causing your symptoms. I think this is less likely.There are some other possibilities with persistent daytime sleepiness when you have started treatment for sleep apnea, including a mixed sleep-disorder, and if it persists may warrant testing in the sleep lab if this wasn't done already..