“When human beings are faced with danger, their adrenal glands flood their bodies with either adrenaline or noradrenaline. Adrenaline energizes the body in the fight or flight mode; noradrenaline creates a freeze reaction, or the numbing of the body and the emotions. This freeze reaction also can be caused by the endogenous opioid system, one of the body’s natural calming systems, which diminishes physical sensations and the intensity of emotional reactions.
As a result of these involuntary physiological reactions, during a sexual assault, the woman doesn’t have the power to decide whether she is going to fight back, try to run (flight), or go limp (freeze). His/her adrenal glands and neurohormones do. The same holds true when she is exposed to a reminder of the assault, also called a “trigger.” When exposed to a trigger, even if she is safe, her body responds as if she is being attacked.
If she responds with an adrenaline surge, leading to a fight or flight reaction, she may experience symptoms such as the startle response, insomnia, anxiety, irritability, and increased nightmares and flashbacks. If she responds with a noradrenaline urge, she may have a numbing or freeze reaction. Or, she may alternate between the symptoms or fight or flight reactions and the symptoms of a freeze reaction.”
(The Rape Recovery Handbook, Chapter 4, Coping Skills)