Angie, you sure are going through one version of absolute misery. And you are not the only one with cognitive impairment -- WHO considers you impaired, and did you have testing? I really would like to know.
I have had sleep disorders including apnea probably all my life, and went undiagnosed for 12 years of specifically complaining of exhaustion, poor sleep, and eventually "I can't think my way out of a paper bag." If I hear one more MD say "well, women YOUR age..." There is some truth to that, but for many beleaguered docs in the age of HMOs and other changes to our "healthcare" system, perhaps it was an easy way out, and no further inquiries were made. Eventually, I didn't habe the brain power to push it, either.
Sleep apnea causes frontal lobe damage in many, and the frontal lobes of our brains are where the "executive functions" are such as you mention, like sequencing activities, planning, follow-through, etc. I had symptoms of early-stage dementia, and watched my parents go that route without any treatment for their sleep disorders. The CPAP brought me maybe 75% back to my "normal" brain (debatable with a life-long condition). You know what brought me back to how I felt 15-20 years ago? And I am a skeptic and have a doctorate, for what that's worth...I heard Dr David Perlmutter on PBS talking about his work and book "Grain Brain." Long story short, I tried his dietary recommendations (and only a few of the supplements -- I eat poorly) for two weeks. After one week, I had enough energy to get through the day...for four days in a row...by the end of the second week, I was firing on all cognitive cylinders. ??? Diet made this much difference? No way! So I went off and ate my usual. By the end of the first 6-8 days, I was getting exhausted again. By the end of two, I was clearly getting "stupid" again. I went back on the plan and stayed there...fell off after surgery, but am back on as of this week.
The PAP treatment I think is crucial, but for some, if not many, of us there are other factors contributing to the cognitive malfunctions. SusanR made some fabulous points and she should know, and Arlene also is knowledgeable, but in addition you might want to go to the library and read Perlmutter's (well-referenced) work and see what you think.
It is terrifying to lose brain function, it is incredibly frustrating for docs to say "but you look fine," and for neurologists to test "what direction would you be going if..." when it's the five errands that must be done but in what order when one thing depends on another, and it all gets utterly overwhelming -- when we KNOW we should be able to do this effortlessly! And never mind the inability to make decisions....
Good luck! You have company in that experience.