Wool BlockThis is mainly seen in Fuzzy rabbits. It is a collection of fur in their stomach. Since rabbits can’t vomit they get hairballs sometimes. The best way to prevent this is to keep them well groomed, and increase fiber intake and always have fresh water supplied. Mineral Oil can be given in the mouth with a syringe. This will help loosen things up so they can pass the blockage.
Bad FeedIt could be bad feed. Check the pellets and make sure they smell fresh and have the greenish color to them. Are the other rabbits eating the food? Diarrhea is another sign of the feed being bad. If your rabbit isn’t eating, and it’s not wool block, it could be a sign of serious illness.
If your rabbit isn’t drinking normally (and it’s not because of a new apparatus to dispense water) seek the help of a vet as it could be very serious.