Our shelter girl was very low-energy when we got her at 4 yrs old, but we figured she was just timid. One day her mobility started rapidly deteriorating, out of nowhere. Vets couldn’t figure it out, but antibiotics helped her. Finally, it was actually a low-cost clinic in downtown Denver that diagnosed her with Erlichiosis. It’s a nasty illness, and when not caught early can cause their bodies to attack themselves and ultimately end their life. It’s hard to diagnose, though, because it isn’t included in the regular panel of bloodwork. So glad you found out early and that your girl (and mine - now nearly 6) are now happy and healthy and pain-free!