@Roberta,
Roberta, my cousin wrote on facebook the same fear.
He has a large family history, but whilst we fear what is passed onto us, it's not always the case. Tiredness, lack of vitamins lots of things can make you "think" you are following suit.
I can't imagine your fear, as I am one that honestly is fearless what ever in life and what ever it throws me, I'm ready. But, I can feel.. Very much so. Live, laugh, .... I forget things at 50
Lots of times.. Write things down but sometimes even our thoughts are so on-going and then there is here, that we forget things that are not important, because we are focusing on the things that are.
Be positive always x