My Cat Suddenly Attacked My Dog.... HELP!?

could be he smelled the other cat or stuff that was on him from the groomer. there may have been stuff going on while you were gone that didn't result in injury. you realy cant know that because you werent there. something may have happened.i would just watch them closely and see if it continues. there is always the possibility that your cat doesn't feel well and doesn't want to be bothered and doggie isnt following the cues the cat is sending and instead thinks the cat wants to play. i hope the dog is okay. you should neuter your pets.it lowers testosterone levels and curbs aggression and also stops unwanted pregnancies.