We create insanity when we indulge in self-righteous anger. Because rage is our ego-creation we have difficulty recognizing it as a mistake. We do not easily find error in that which we create. The Course says you love your recreations. Every response you make to everything you perceive is up to you, because your mind determines your perception of it.
Rage is an ego construct.
The ego arose from the separation, and its continued existence depends on your continuing belief in the separation. Rage is a separation technique. When out of control we, like Arthur, place ourselves on a piece of Mars. Out of sheer exhaustion we may come out of rage only to realize that we don't know why or how we got there. It is as if there is a built-in disassociation from the event as we fall back to the first instinct, survival.