Flowers for Algernon.
Briefly, this story follows, through first-person journal entries, a test subject for an experiment in surgical procedures to raise "intelligence" in human subjects. The test subject and journal author, Charlie Gordon, experiences a rise in comprehension and ability from severely handicapped, to genius-level, and a subsequent fall.
This is an important work for the genre, raising questions about the nature of intelligence, informed consent, personal dignity, and personal rights of the handicapped. (It's also one of the few examples I can think of where a short story has been successfully expanded to full novel length)
This entry, however, is not about the story itself, but about one aspect of Charlie's perception of his fall from the heights the surgery had propelled his mind. Charlie does not remember the heights that his mind had attained, and remarks that he had been told that he was "smart."
Several decades ago a friend of mine, a fellow software engineer, began suffering symptoms of now is recognized as Early-onset Alzheimer's. He was in his mid/late-forties when he started to be more forgetful, his work performance suffered, his anxiety and depression (a per-existing condition) increased markedly, and his life started to fall apart around him. There was some delay before any kind of a meaningful diagnosis was found - the thought was that it was his existing medication for depression that was causing the issues, not a separate organic cause. He and his wife had had only one child, who was by this time grown and on his own.
Because of their financial situation, his wife was able to quit her job and become his primary caregiver, which is a task I certainly did not envy her. The progress of his decline was fairly rapid, barely 7 years from the time he started to be noticeably disorganized to when he could no longer reliably bathe himself or use the toilet. Along the way he, of course, lost his job, and they had to turn to pricey private medical insurance to defray costs after his COBRA eligibility ran out. It was probably 3 years before a diagnosis of Alzheimer's Disease was finalized. On one way it was a relief, as he was feeling that he was going losing his mind. Unfortunately, in a different, but very real sense, that was exactly what was happening.
And, unlike Charlie Gordon, he knew what he had lost, and could feel it slipping away from him, week by week and day by day. He knew that he could do certain things, and could no longer perform those tasks. He lost the ability to play the piano or read music, and would sit at the keyboard trying to puzzle out simple tunes. He knew that he had had a good career, and that he was mo longer able to work, and being someone who had grown up in a time when men were assumed to be the ones being the primary breadwinner, that ate away at him. He even attempted to take his own life, before even that ability was lost to him.
His frustration and depression turned to rage, usually directed against his wife and son, and then he didn't even recognize them for who they were, mistaking them for siblings or his parents, or even not recognizing them at all.
When he finally passed on, about 5 years after the definitive diagnosis of AD, his wife had finally had to pass his care on to an institution, and she was actually, after a fashion, relieved. Before someone gets all up on a high horse about that, remember that, during all this time, she stayed by him, even though the person she had married, who was the father of her child, who had been the other side of their married life was gone. Gone for years, as the AD took him away from her. She still loved and cared for him, but it was the love and care for her family member, because her husband, her life mate was no longer in that earthly shell. And now, at last, she could mourn the man who has passed, who had actually passed years before that shell ceased.
I honestly don't know how I would hold up if I were in that situation, knowing that ability was slipping away, and that there was no chance to reverse, or even halt, that progress. It just seems to be the cruelest disease of all for that aspect.
I would hope I could face it with what dignity I could muster. But I really don't know. And I pray that I never have to face that question.