It’s possible to have ADHD and Sleep Apnea (Exhibit A: my husband). The difference is that if a neurotypical person develops sleep apnea, they may still be able to function, whereas an ADHD person barely does (and my husband will debate the “barely” also — he forgets many things when he travels, but never his CPAP machine, and is religious about using it). If you snore and/or fall asleep within seconds of your head hitting the pillow, you (anyone really) should get checked for sleep apnea.
There are books about executive function for adults which suggest ways to break down a problem and address it. There was also an this interesting one about planning your tasks/day through visualization (https://www.amazon.com/Weeks-Organized-Life-AD-HD-ebook/dp/B009R6GEYO/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1497303061&sr=1-1). I will never be able to plan a whole day in advance — are you kidding me? — but I use his visualization technique all the time for projects that I may never have started otherwise (and even to reset myself during the day, when I suddenly have no idea what I am supposed to be doing or even what I am currently doing). I found that by visualizing the next moments or next set of tasks I can proceed without tripping over feelings (and I have plenty of feelings of all sorts, most negative).