Ever totally lost it?
Have you ever found yourself so mad that you just "loose it", you shout and scream or slam something.
At this moment, your thinking brain has been switched off.
We have different parts to our brain, at the bottom is the part we use in an emergency, it responds very quickly and focuses entirely on keeping us alive. Our top brain is the one that makes us different from other animals, it allows us to think things through and make good decisions.
When the bottom brain decides that you are not safe, it takes control and shuts down your top brain. You are no longer able to think like a human, only like a lizard and the lizard brain only has a couple of options: fight, flight or freeze.
So... when you loose it, your lizard brain has switched off your thinking brain and is now in "fight" mode, hence the shouting and big body movements. You think you are fighting for your life.