I had a huge persian called Mortimer that I had to have put down. He was only 3 years old, and one evening we heard a pitiful meow from the bushes. His back legs were paralysed, and he had lost control of his bodily functions. We had him extensively examined, and not a thing could be found wrong - i.e. no bruising, no breaks, no internal damage. I cried for ages, I held him as they put him to sleep!!!
We buried him in the front garden - found a lovely spot under a tree, and I dug what I thought was a substantial hole, but my wife wanted it to be deeper. The next strike with the shovel went through the water mains!!! Needless to say we found a new spot for him!!
Losing a pet IS losing a member of the family! I share your pain, and wish you well.
Bull!