Why are my dogs being aggressive towards each other after being spayed?

I had my dogs spayed yesterday. They're sisters and have been together the entire 8 months of their lives and seem to have been great friends. But today, now that they're home from the vet, the keep growling aggressively and trying to attack each other. Is this normal???

its called Hormonal changes

They just had major surgery & are in pain & feel bad & still under the effects of being under. Naturally they are irritable & feeling hostile while they are hurting. In a few days when they start healing & effects are wore off, they should start acting better. Females even littermates will fight each other as they become adults. You did the best thing with having both fixed now. Keep them separated til they want to be together.