Fight or Flight | The Physiology of Fear

Your heart starts pounding, your muscles tense up, breathing quickens, and you start to sweat. Do you run or do you stay and fight? Fight or flight evolved as a mechanism for survival, allowing humans and other mammals to survive life-threatening situations. But what happens to this system when it’s exposed to a 24/7 news cycle filled with stress? What happens to this system when the threats are more abstract than tangible? 

The technical name for what’s responsible for the fight or flight mechanism is the sympathetic nervous system. The sympathetic nervous system pairs with the parasympathetic system to form the autonomic nervous system (ANS). As a whole, this system manages and regulates all the functions in your body that happen subconsciously – in our practice, we often refer to this as our body’s automatic operating system, or aOS.

The Merck Manual defines the ANS as follows: “The autonomic nervous system regulates certain body processes, such as blood pressure and the rate of breathing. This system works automatically (autonomously), without a person’s conscious effort.”

The autonomic nervous system controls internal body processes such as the following:

• Blood pressure
• Heart and breathing rates
• Body temperature
• Digestion
• Metabolism (thus affecting body weight)
• The balance of water and electrolytes (such as sodium and calcium)
• The production of body fluids (saliva, sweat, and tears)
• Urination
• Defecation
• Sexual response

The sympathetic division prepares the body for stressful or emergency situations—fight or flight.

The parasympathetic division controls body processes during ordinary situations. It slows the heart rate and decreases blood pressure. It stimulates the digestive tract to process food and eliminate wastes. Energy from the processed food is then used to restore and build tissues—rest and digest.

Your sympathetic and parasympathetic divisions are dance partners that react and respond to the demands put on your body. When everything works well there is harmony (homeostasis) – neither dance partner steps on the other’s toes. But what happens when the partners are not in sync, when one side weakens or dominates? If one system dominates it prevents the other from working optimally. Here are some of the symptoms and signs:

Overactive Sympathetic

• Anxiety
• Episodes of a racing heart
• Easily startled
• Difficulty relaxing or sleeping
• Sensitivity to bright or flashing lights

Weakened Sympathetic

• Low blood sugar
• Low blood pressure
• Low pulse rate
• Fatigue
• Weight gain
• Low libido
• Frequent colds or sinus issues

Underactive Parasympathetic

• Chronic digestive complaints
• Bowel or bladder incontinence
• Constipation
• Dry mouth
• Difficulty swallowing supplements or bigger bites of food

The fight or flight mechanism was never meant as a long-term response to chronic stress. We were only meant to visit this state when our lives were in danger or when faced with acute exposure to a stressful or scary situation, not live there for days, weeks, or even months on end. When we are consuming a constant barrage of negative news, when we live in a stressful environment, or are trapped in a bad relationship we are triggering the sympathetic nervous system. 

Over time, sympathetic dominance wears away the flight or fight response and leaves only the parasympathetic system to manage the body. Imagine driving a car with only the brakes but no gas pedal. 

This is what happens when we live in a constant state of fear. It causes not only mental duress but it causes systemic bodily harm. 

Here is the good news – abstract fears are easy for us to manage. Avoiding the repetitive bad news loop, practicing mindfulness, and expressing gratitude are simple and healthy steps that bring balance to our autonomic nervous system. Thankfully, the majority of us are not under mortal danger and the rest is under our control!