I recently went through this. I was diagnosed with ADHD 15 years ago and have been managing it, but over the last 2-3 years I had been experiencing increased levels of brain fog, fatigue, and by ability to focus had deteriorated to the point I wasn't sure if I would be able to continue working. I had a sleep study done 10 years ago that only found Night Terror Disorder, but no signs of sleep apnea. I did another sleep study about 6 months ago and it turns out while I wasn't having apnea events I had constant and persistent hypopnea. Started using a CPAP and it feels like I've been given a second lease on life. FWIW, I am a very active and in shape individual within a healthy weight range. Don't wait to get tested if you have even the slightest worry you may have it.
What machine and mask do you have? I had a bad CPAP experience 2017ish and navigating sleep apnea treatment with ADHD kinda sucks. I got a recent sleep study done, but the doctor's office seems like a sales farm for a specific CPAP brand/model and they aggressively steered me away from an oral appliance.
I was prescribed modafinil earlier this year and it worked well when I took it but it was intense at the useful dose so the doctor put in for a sleep study. It was a 3 month wait but I am finally getting it done next week an I'm hopeful it leads to a conclusive diagnosis.
I also noticed my issues were worse after my 3rd bout of covid :-/ I had very high sensitivity to alcohol and caffeine after the 2nd bout and have largely cut both out of my life (I never drank more than 20 drinks / year in my life anyway).
Doesn't even need to be a CPAP. I had a sleep study done and it said I basically only had sleep apnea when lying on my back, and my doctor suggested a dental appliance to pull my lower jaw forward.
I got one from my dentist for way too much money, it broke, so instead I got a "snore reducing mouthpiece" from ZQuiet or SnoreRX which is basically the exact same thing but they haven't done a clinical study to show it reduces sleep apnea. I wear one every night along with a nose strip (like Breathe Right, but a different brand that I like better) and my mornings feel like I was hung over are long gone.