The key, IMO, is regular checkups and listen to the doctors. Sure, if it's something serious, get a second opinion but be forewarned.
I have noticed with people in my family, that as you lose mental function, you revert to your inner self. It can be angry, happy go lucky, or anything else. There are people with Alzheimer's who are the happiest people on earth, and there are people who are violent, dangerous people. I am not sure who my inner self is, I hope not violent.
I heard Reagan thought he was being made fun of when they told him he had been President. He became quite angry about it.