If the cycle of illness doesn’t stop, start looking for Addison’s or Cushing's disease.
You might recall a case where you couldn’t quite get to the bottom of problem, a dog repeatedly presenting over a period of weeks, months or even years; the owner describing a dog that wasn’t quite right, but with nothing drastically wrong. The dog might have responded to nonspecific therapy, such as intravenous fluids, and been discharged… but then returned to the practice weeks later exhibiting the same signs.
If you have ever found yourself treating the same dog over and over again, it might be time to look beyond the obvious.