Lady is a 10 year old Yellow Lab/ Golden Retriever mix. The last 3 days I have noticed that when she is going downhill, her hind legs seem to not work properly, she sits almost involuntarily. Then she will get up and go off like nothing happened. If the hill is steep it may happen again, and it seems worse today than it was 2 days ago. She does not seem to be in pain and walks normally going uphill or on flat ground. It seem the extra weight transfered to her hind legs when going downhill causes the problem. Any ideas?