The concept of "mental health" in our society is defined largely by the extent to which an individual behaves in accord with the needs of the system and does so without showing signs of stress.
God may allow His servant to succeed when He has disciplined him to a point where he does not need to succeed to be happy. The man who is elated by success and is cast down by failure is still a carnal man. At best his fruit will have a worm in it.
It is the quietest and meekest people who are often capable of the most sudden and unexpected violences for the reason that when their control does snap, it goes entirely. (Hercule Poirot)