Yeah always take them to the vet if they don't eat or poo for 12 hours or more - stasis can turn serous pretty quickly.
Have the temps changed at all where you keep him? Sometimes if my bunnies get a little warmer than they'd like they're not as active. Has anything else changed that could be affecting him? If he's still eating, drinking, and going to the bathroom normally, those are good signs.
If he doesn't seem like himself for much longer though I would get him to a vet. Bunnies are good at hiding when something is wrong- signs of pain can include being larthagic, sitting hunched up, and/or grinding teeth.
Good luck! I hope little Henry is back to normal soon.
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