A bunny can absolutely get a bout of tummy trouble, come out of it and stay healthy. Its not uncommon when a bun molts f ex. Stress can also spark a gut slowdown. A ppoorly bun tends to get hypothermic, and hypotherma causes the symptoms to worsen further. Many buns can be perked up with a heating pad, fluids and Critical Care until they start eating on their own again.
Sometimes a minor gut slowdown causes gas to form in the gut, and that hurts if it can’t escape. The bun stops eating, sits hunched up or presses its belly against the floor almost like it was doing push-ups.. A standard first aid measure is to give 1 ml of baby gas drops (simethicone). It’s ok to give on suspicion of gas according to Medirabbit, and surprisingly often it turns a bun around in 20-30 minutes. It’s good for all bun owners to keep in the first aid kit.
If your bun gets repeated tummy trouble, you should start thinking about causes.
You will of course need to keep a rather close eye on him for the next few days or so. Put fresh litter in the litter box often so you can keep track of amount, size and consistency of poop. You should make sure he eats and drinks normal amounts. It’s especially important that he eats hay.