i went through the same thing with my granny, she had Alzheimer's and cancer she was in the 4th stage when they found out.
it's hard. i dont have a clue how to explain it to anyone.
Its like one day there fine and then the next there totally different..It's a rough thing to go through, and especially when you are as close to your granny as anyone else..
that was prolly the worst day of my life when i lost her on May 1 2006.

But i'll be praying for you man..