Well, I hope you realize I wasn't making sport of the tremendous number of people who suffer cognitive decline, but of my own IQ (and as hinted at in a reply, someone else we all might have heard of).I have no idea what the questions were** (though the score was out of 30), but my father had to do a test to assess his cognitive abilities. He scored, I believe, 6***, thus placing his Alzheimer's in the worst of the three categories. (My mother said that he was almost crying when he heard how badly he'd done. (He wasn't the sort of person who ever shed a tear; it wasn't until much later in the progress of his condition that I first saw him (silently) weeping, and that was when he was well into his 80s.)
Now I'm not sure how useful the measure I'm about to use is for the rest of you, but my father was, before his condition set in, more clever than I am (and more diligent in applying it), so I can see why he was so upset by "failing" the test (as he saw it).
** - I've heard that one of the questions in the UK is the name of whoever is the current UK PM... but whether or not that's more than just a rumour, I don't know.
*** - It may have been 4. (My memory isn't what it used to be.... )
What you bring up is I think the crux of it in such a situation...one ALL of us I bet will experience. It's bad enough to recognize the loss of what once made the world so clear to us, but the frustration it brings in our daily lives. That frustration, IMO is the worst part.
Many of us use reading glasses now that we're older. For those that do (and don't have them integrated into constantly worn eye wear), you might recognize the frustration of attempting to perform the simplest of tasks you have a thousand times before...but now before you can perform this 5-second task, you have to stop and find your readers. So, physical limitations will vaguely hint at that frustration.
More to the point, as I mentioned in another thread, now that my knowledge is expanding on how to tell the stories I want, I find my chiseled in stone memory eroding--which was something that helped me to cope much of my life. I might not have had an education, but I could recall what I had seen or heard in exacting detail. Well, that's fading fast and is all but gone. In addition, after working so hard to build an extensive vocabulary (as an example), I'm finding that much of what I learned, I'm of late beginning to forget rapidly.
I believe...the reason is oxygen deprivation due to respiratory issues which I refuse to compensate for--recognizing on difficult breathing days I cannot think clearly--but, there is nothing I'm willing to do to change it. So, just as what I finally hoped to accomplish--to simply accomplish something--is within my grasp, I find it slipping away faster than I can do what I want/need.
That frustration I suspect is extremely minor compared to what someone like your father feels. And yet, my petty self-inflicted decline feels crushing.
So, though 'I don't know,' that frustration I suspect is what hurts folks most.
My prayers he can find ways to work around his difficulties.