Yeah, we took in a litter of puppies and after having them de-wormed their stools literally turned into liquid and worms, and there was lots of it.
Chances are it's just one of the side effects of the de-worming process, but to be on the safe side you could look for a vet's office that is open on Sundays and maybe they could answer a few questions for you?
If it is a usual side effect and they care about animals they should have no problem putting you at ease.