Not sure. She has in the past over exerted herself on a walk and had trouble with her hind leg being sore/stiff for a day or two. The family that watched her said that she walked a lot on Wednesday night, so this is longer than usual for her to have an issue. Plus, on Saturday, I had to lift her hind section off of the ground in order for her to stand a couple of times - and that's really unusual. I've started giving her buffered aspirin again to help out. They weren't home when I went to get her Friday late afternoon, and she could barely get up to leave. Real nice family, but I'll be asking my friend...in general..."wtf?"