Is he by chance a mix rabbit with a lop eared parent? Does the head shaking seem excessive and does he seem to be scratching at his ears a lot? Can you see any debris in his ears or do they smell at all, and can you feel any bumps or warmth around the base of the ears? Is he eating, drinking, and pooping normally? Does it happen to be hot where you have your bun? Could he have hit his head on something? Has he been to the vet recently?