Causes
Anything that reduces food intake or gut movement: a diet low in hay, stress, pain (dental or of another origin), dehydration, lack of exercise, obstruction. A rabbit's gut must NEVER stop.
Diagnosis
Examination, X-ray to assess gas and content, and a search for the cause (often dental or pain).
Treatment
EMERGENCY: rehydration, pain relief (pain slows the gut further), prokinetics to restart transit, syringe feeding of a formula specific for herbivores, and treating the cause. The sooner action is taken, the better the prognosis.
Prevention
A diet based on hay available at all times (80% of the diet), constant access to water, daily exercise, stress control, dental check-ups, and grooming during the moulting season.

