Do you know what type of painkiller he was given before he was sent home? It was buprenorphin, this could be a side effect. It can give drowsiness that lasts quite some time. If it was Metacam, I’d be slighly more worried. Have you seen any poop? Has he been eating anything near normal amounts? If he has eaten only very little, syringe feeding Critical Care or soaked pellets made into a mush is necessary since it’s been 32 hours. The pellet mush/Critical care can be mixed with something yummy to increase appetite. Did the vet send you home with any pain meds to give him at home?
It’s good you have him inside, because hypothermia is a common issue post anesthesia in rabbits. They can get cold indoors too, if they don’t eat, because their cecum (part of their intestine) is a “heating-factory” that keeps the bun’s body temp normal . It only works if the bunny eats though, or there’s nothing to make body warmth from. You could try offering him a warm water bottle or handwarmers wrapped in a blanket, he might like it or he might not want it. He must have space enough to move away if he doesn’t want it.
For a boy that young I’d rather expect a quicker recovery, many young boys are acting quite normal, almost as if nothing ever happened, when they come home from their neuter. All buns are different though. It’s very good that he’s eating. Have you checked the incision site? Sometimes there’s blood/fluid leakage into the scrotal sacs. One or both sacks can be get pretty big and the condition should be seen by a vet.
I’d give the neuter-vet a call and ask, but first check the surgical site so you know what to tell them. You can’t really determine a bunny’s core temperature by feeling its ears, but you can get a tiny bit of an idea if the ears are ice cold or very hot. They should be neither, although for a resting bunny, cold-ish ears are normal (unless it’s very hot in the environment).
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