I mean, there's a lot to process here. It would depend, do I keep my present knowledge and intellect? Do I keep the abilities of the cat or dog? What about knowledge like how to hunt or eat? Why was I changed? What's the environment? Etc.
I'd scream "oh no!" so the wicked fairy wouldn't figure out it's fun for me and change their mind, and then I'd just chill with my dog or cat life. If I could be taken care of by a trusted person or people, that would be great.
I remember reading a book when I was a kid called The Dog Days of Arthur Cane. I think the fairy was a witch doctor but basically the same idea. As I recall, Arthur saw the best and the worst of humanity during his predicament. Sadly no Wikipedia page for the author but the book is on Goodreads: https://www.goodreads.com/book/show/2006378.The_Dog_Days_of_Arthur_Cane