My kitty died unexpectedly

My kitty of 11 years died unexpectedly Friday. I awoke to the sound of her moaning in distress. When I found her, she looked alarmed. I picked her up and she went limp in my arms. On the drive to the vet, her mouth opened and her tongue was out. The vet said she was severely dehydrated, likely for more than 24 hours. She was extremely limp and weak and in pain. She lost her urine, but her urine was clear.  The vet said that was a bad sign, indicating the kidneys weren't working. He curtly told us she was dying. He offered hospitalization, tests and aggressive treatment, which he didn't believe she would survive, or he said we could take her home and try to nurse her with pedialite, antibiotics, baby food and pain medication, which is what we did.  But at home, she declined rapidly- Becoming disoriented, unable to walk, crying in pain, etc. She died about 6 hours later. The vet said the urine analysis (but who knows what they tested it for) "suggested some diabetes," and that "there must have been something going on with her kidneys." That's it. She showed ZERO prior signs of kidney failure. She showed zero signs of ANY illness.  I know they hide it well, but kidney failure does produce signs. We are confused, shocked and heartbroken. What could have happened? In the absence of any real information from the vet, I'm hoping someone here can offer some insight.  Please help if you can.  Thank you......

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