Sue- I'm just reading this now and my heart goes out to you. I had an almost identical experience with my Sheltie, Grizzy Bear, about 10 years ago. Out of the blue, he had no use of his hind legs and would not eliminate. We let it go for 2 days at the Vet with vigorous testing, and we decided to let him go. It was heart breaking. Big hugs to you.