I had something similar once with my rabbit Sugar, he stopped eating, went all limp etc I thought he was on his way out as he was old so kept him warm and just kept trying to feed him, eventually he ate carrot tops and then after that kept eating and was fine again in a couple of days.

When I took him to the vet she said something must have stressed him out which had caused his guts to stop working (the stress of your other rabbit dying may have done this) sometimes their guts start up again and sometimes they dont I would take him to the vet as they may be able to give something that will get things going again...if this is the problem.

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