Nice question. Water travels to the hypertonic side and in the Addison crisis, you would be hypotonic. Also, water in the gut is reabsorbed in the gut through osmotic diffusion so it is dependent on the osmotic gradient caused by sodium absorption. So if there is low sodium and it is not being absorbed but instead being removed, this osmotic gradient seizes to exist and water cant be reabsorbed. Lastly, the gut has receptors that respond to osmolarity. Since the body is unable to maintain osmolarity by absorbing sodium maybe these receptors respond to dangerously low osmolarity by getting rid of water instead?
