Not alzheimers but might as well be

My 87 year old father was recently admitted to a hospital for pneumonia. Unrelated complications occured and he went through a dangerous and traumatic surgery during which his gallbladder was removed. He was in ICU for almost 3 weeks.
He was released to a regular room yesterday and I noticed something funny about his cognition. He was confused and even seeing things (not big halluncinations but small things).
Today he is completely disoriented and delusional. He wasn't even sure who I was. He has all these paranoid delusions that me, my brother, and my mother (who died three years ago) are trying to sue him for all his money and that he is in prison and I am responsible.
In other words he went from about a pre-hospital stay baseline of 95% normal mentality to something less than 15%.
I know it isn't Alzheimers (he was cleared of that diagnosis years ago, and I don't know if all these symptoms fit the Alzheimers profile).
What I'd like to know from the children of Alzheimers patients, is how do you handle it? Not the interacting with the parent afflicted, but how do you handle the abject cruelty of the disease and the deep deep sorrow and pain. Although we are now waiting for some tests to see what is going on with my dad, I may find myself in the position of having a severely disoriented parent.
I am already not handling it well... I couldn't stay with him longer than 30 minutes today. I can't even worry that I am over-reacting because the situation is just as upsetting as I think it is. I have spent the past 10 years taking care of my parents, the last 3 just my father. We are very close and as I said, for 87 he is pretty sharp. Was pretty sharp.
As I write this I guess there is no answer. Watching a loved one lose the function of their mind is just the most awful thing ever. No way to get through that unscathed.

[iam1butterfly]

I empathize.
My 88 year old father went through something similar last month. He had open heart surgery (heart valve replacement and 1 bypass) and suffered a minor stoke during the procedure. He's now totally befuddled; has considerable memory loss; and now must adapt to the physical limitations of partial paralysis.

It's difficult watching the mental and physical decline... but, the change is even tougher
for my dad as he was so independent before... and, now must depend on the kindness
of others.

What I've done is that I've accepted the mental/personality change(s) as a byproduct of both the medical procedure and the aging process... and, I don't personalize it.