Duggeh so sorry to hear that.
I was in my mid 40s before I experienced a close loss like that. It was my Grandmother, and I know exactly what you mean by "horrible and alien experience", it was like seeing someone else inhabiting her body. She was not there anymore, just a shell with some poor woman in pain. That's when I discovered that they need to wait until a family member tells them to give her all the morphine she needs to be comfortable. They can't suggest that legally in this country.
One week after my Grandmother passed, one of my favorite Aunts passed away, then just 9 days from then my Father died. It was the worst month I've had on this Earth. Especially since like most men there were too many unsaid things between my Father and I. I felt like a zombie for weeks.
But you get through these things, and you get stronger because of them. It didn't prepare me, but it did make it at least more familiar a few years later when my little 5 y.o. Nephew passed. That was the toughest of all!
I don't know much about your Grandfather, but I know a bit about you old bean, and I know for certain that you made your Grandfather a very proud man indeed! You're a good guy Doug, and you'll find a way to use this experience to be an even better, more empathetic man.
My glass is raised to you both!