That happened with ur Oreo in the last year of her life. She died in June of 2012. She was a black lab/greyhound and would fly like the wind over any terrain, and would come home sometimes limping with a hurt paw. We have 10 acres so she wasn't roaming on anyone else's property. She was bitten at one point by a copperhead or black widow; we never knew which, but she rebounded. She was mostly blind in her last year (died at 15) and seemed awkward in the snow even though she loved it always. I agree with Cgrandma. It is hard for us to watch our animals decline. I know your concern. Just let your best furry friend do his thing even if he falls down. Believe it or not, he is happy no matter what. Maybe, it is joint issues. Oreo had that, too, at the end. Have you tried glucosamine for dogs? But, at least, we know we gave them a wonderful life.