It's true... if you are over worked and over stressed, you are one step away from a psychotic break.
I know... because I have/had one of the most brutal work ethics ever...
The brain is like any other muscle in the body, work it too hard and it cramps up, work it to it's absolute limit and you will hit the wall.
http://en.wikipedia.org/wiki/Hitting_the_wall

Such fatigue can become seriously debilitating; in cycling, exhaustion can reach the point where the cyclist is unable to stand without the support provided by the bicycle. Symptoms of depletion include general weakness, fatigue, and manifestations of hypoglycemia, such as dizziness and even hallucinations. This condition will not be relieved by brief periods of rest.