The Body's Alarm System.
Our brain instantly decides the best way to deal with the perceived threat:
FIGHT: when we need to fight our way out of trouble (adrenaline)
FLIGHT: when we need to escape the danger (adrenaline)
FREEZE: when we need to be immobile and numb (adrenaline)
FLOP: when death seems almost inevitable, the parasympathetic system activates the relaxation response - thinking processes shut off, heart rate slows, muscles relax, causing collapse and submission
FRIEND: when we need to socially connect with the threat (giggle or smile, try to befriend attackers etc)
These are all normal responses to threat. When our brain learns that a response seems to work for us, then our brain will tend to always use that same response.