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.