My Great Aunt has alzheimers, she got a lot worse after my Great Uncle lost his battle with Cancer. She has great long term memory, can recall things from many years ago, but ask her about an hour ago, nothing. My cousin tried to take care of her, it got bad. They finally had to put her in a home.
It is hard on those that are closest to the ones suffering. I feel sure my uncle knew something was wrong, but tried to deal with it on his own.