Very similar experience with my mum. The fear and panic at the gradual loss of 'who they are'. People say "you won't know what's happening" but actually lots of people do know because the beginning is a very slow long slide of small things.
Like mum stopped popping to the shops for small items and got the grandkids to do it for her. She said it was because she couldn't be bothered with the walk and at first we believed her. It wasn't till much later we realised she'd got lost on her way home a few times and frightened herself, so her world just got smaller and smaller as she did less and less.
Mum had it for at least 10 years before she had really incapacitating symptoms. By then she'd gone through stages - massive anger, physical and verbal aggression, sulking, losing things, leaving herself notes to remind herself of things, constant forgetting of people, places, dates, appointments, days of the week or 'remembering' but it was all muddled and wrong and then refusing to be corrected, giving her belongings away then claiming it had been stolen, getting massive health anxieties, constantly at the doctor, forgetting to eat or drink for hours, even days. That's all before she went in a home. It's awful and she did know what was happening a lot of the time.
Though for some it can be very fast as well. I know someone who went from busy, intelligent, well educated, travelling the world businessman to in a home not recognising his wife in 6 months.
I genuinely think all this talk of diet, exercise, mental stimulation etc is an exercise in hope over experience. It may stave it off a bit and will help with quality of life as we age, but it won't stop you getting it, if that's what you are destined for. Some will be lucky and some won't. It's a lottery. We are all living so much longer for a start, so more if us will get it. I'm really worried about it but just there isn't much you can do to stop it getting you in the end - or you might not. It's just luck of the draw.