I am very grateful for and comforted by these lovely messages from every one of you.
When the first lot of tests came back, it was clear that his severe collapse was not due to his kidney disease, as first thought. He had suffered what is called "a saddle thrombus" which is when a blood clot travels from the heart and blocks an artery to the lower limbs, disabling movement in the back legs.
It is an extremely painful condition and not many cats survive it at that severity. However the odd one does, and meantime he is receiving critical care while they wait to see what happens. If the clot resolves/dissolves, he may live up to another year, though will always be in danger of another clot forming as he has a heart murmur too.
I was prepared to let him go yesterday because of the pain though the vets said no, let's do all we can first and then review the situation.
He is on continuous pain relief though he still seems to be quite uncomfortable - though not in the agony he was yesterday.
So we will be reviewing the situation in a few hours' time. I will choose whatever is best for him.
I have been visiting him and have just come back. He rubbed his cheek against my face, which is so typical of his super-affectionate nature. I will let you know what happens. He may make it, he may not. Maybe your prayers helped him a lot. I think the vets were a bit surprised that he survived the night. So there is some hope there, not over yet...