in my personal experience this is not uncommon - again, wud hav to look at u to be able to say anything definitive;
I've wondered about that for some time; don't they? animals are very sensitive to owner's mood - if the owner gives the pet a medicine that makes the owner feel better about having done so, I wouldn't discount the pet picking up on that and having a "placebo" effect occur as a result (owner happier = pet happier)...