Also, patients with early stages of dementia are damn good hiding their decline.
My father's mother had Alzheimers later in life and my dad has shown some signs of short-term memory loss, although they might be different since he's had mini-strokes and issues with ammonia buildup, which is basically the body poisoning itself. In many ways, he would show signs that were similar to what you read about hypoxia: that the victim doesn't actually know anything is wrong, so they continue to function at lower and lower levels, continuing to be unaware that anything has gone wrong.
For example one of the signs something was wrong was that while my mom was away on business, my dad attempted to mail a letter, only to have the post office return it because he did remember to put a stamp and pre-printed return address sticker on it, but the hand-written address was totally unintelligible. Like, literal giberish scribbled on the envelope. He had no memory of having done this because his brain was unable to determine there was a problem.
If you read up about hypoxia, you'll see that the first thing that goes is judgement. Around the same time, the ability to do math in your head goes away. For pilots who undergo hypoxia training and analysis, one of the things they'll have them do is simple math by hand. Often times they actually think they are fine and then realize they are unable to do math in their heads anymore. If the effect is pronounced enough, they will already be too far exposed and just write a wrong answer, blissfully unaware that anything is wrong. The control observers usually use that as a key to note that the experiment is being failed and they need to be put on oxygen. I don't doubt that hypoxia's effects are not too far different from dementia and Alzheimer's. I could easily see someone who can no longer do math in their head and has lost the ability to quickly do judgement calls like "Do I need to spend $300 on software that says it makes my computer run faster?" make the wrong choice, blissfully unaware of there being a problem.
There was another thread on here somewhere regarding healthcare and especially final stages of life. I don't think I ever did reply in that thread, but ultimately we're reaching a point in the advance of society where we're physically able to keep people alive and functioning who are not able to care for themselves. This is really a very recent innovation in the ten thousand or so years of organized societies on Earth. It's something we're going to have to deal with one way or another.
To the OP, I wouldn't beat yourself up. You are dealing with the same difficult situation that a huge number of people are running in to now, as another recent thing seems to be the notion of old people having huge piles of cash. Even just a generation ago, like my grandparents age, they didn't build up cash reserves. They had Social Security, a lot of them had military pensions (being the WWI & WWII generation, with so many veterans) and usually standard pensions too, because that's how it was done from the 1920's through 1960's especially. People had pensions, even 3 or 4 pensions, each with a modest payout that continued until death. Now in the modern era with a lot of workers having 401k's and IRA's and personal savings, retirement looks different now from what it did even just 20 years ago. Now there need to be more safeguards in place for all these new generations of workers with lump sums of cash rather than steady monthly pensions.
