Did he stop eating in the last day or so, or maybe was not eating very much and not as active as usual? Is his water supply ok? If he drinks from a bottle with a nozzle, have you checked to make sure the nozzle isn't stuck and he hasn't been able to drink. A rabbit that doesn't drink, won't eat, and a rabbit not eating will not poop as much. Though it sounds like now he is eating normally?
Have you changed or given him any new foods recently, or have there been any major changes in his environment like moving him to a new area, getting a new pet, or maybe loud sounds around where he is?