Mental illness is certainly common, but someone who is normally able to cope ok can be pushed over the edge when under too much stress, and even who initially has no mental health problems at all can end up being driven to insanity, given the right conditions.

We need to be treating mental health just as importantly as physical health. There's all sorts of OH&S guidelines for proper posture, lifting things etc. Similarly, there should be OH&S guidelines for ensuring employees are provided with a safe working environment in which they're not going to end up like this (at least, to the extent that work contributed to their condition).