How would a doctor treat himself if he had cholera?

Hydration: Hydration and if necessary antibiotic prescription by a colleague.

Poorly: The old saw is that a doctor who treats themselves has a fool for a doctor and a fool for a patient. On the other hand the best treatment for cholera is rehydration with fluids that contain electrolytes and sugar. The latter is essential. Usually antibiotics are contraindicated and well-fed healthy persons usually recover from this quite rapidly.

Fluids: They would drink a solution of water and salt to replete their body fluids. Most people die from dehydration which can be treated with drinking a salt and glucose solution.