Understanding the Fight, Flight, or Freeze Response: How Anxiety Affects the Brain and Body

In mental health therapy, we often explore how the brain and body respond to perceived threats — especially when anxiety is involved. One of the most important concepts to understand is the fight, flight, or freeze response. This is the body’s built-in alarm system, and while it’s designed to keep us safe, it can become overactive in modern life, triggering intense physical and emotional symptoms even when there’s no real danger. By learning how this response works, we can better understand the way anxiety shows up and start building more trust in our bodies.

The Brain and the Fight, Flight or Freeze Response

• The amygdala area, or reptilian mind, is the oldest part of the brain. It controls the fight, flight or freeze response. Its job is to protect, with no regard to comfort or happiness.

• Since prehistoric times, the mind has been wired to seek out potential threats. The world early humans lived in was often a life-or-death place, and “what ifs” were part of a lifesaving process that developed to keep us protected. “What if that noise coming from the bush is a predator? I should run away!” In those times, it was better to be cautious and guarded than to ignore the internal alarms.

• The fight, flight, or freeze response is set off when the amygdala has been triggered by the merest hint of possible danger. It would rather set off a thousand false alarms when there is no actual danger than miss just one real problematic situation. Its motto is “I’d Rather Be Safe Than Sorry.”

• The system was designed to keep humans safe in times of danger, but it can become confused and misdirected. It can start to misidentify safe things as dangerous, or even allow the thought of something dangerous to sound the alarm.

• A regulated nervous system sounds the alarm when there is actual danger, such as a car swerving dangerously on the highway. A dysregulated system, or overly anxious system, reacts and sounds the alarm in situations that are perfectly safe.

• Today, humans are fortunate enough to rarely encounter life-or-death situations, so the mind often turns inward looking for those same life-threatening scenarios — but they are almost always imagined or exaggerated.

The Body and the Alarm Response

• When the body has perceived a threat, the amygdala sends a distress signal to the body’s command system (the hypothalamus), which signals the adrenal glands to begin pumping adrenaline into the bloodstream.

• The wiring is so fast and efficient, the amygdala and hypothalamus start this flow even before the brain’s visual centers have had a chance to fully process what is happening. That’s why people jump out of the path of an oncoming car even before they realize what happened.

• As adrenaline circulates at a rate of three feet per second, it brings on several changes felt in the body. Breathing gets faster and deeper so the lungs can take in as much oxygen as possible. The heart beats faster than normal, pushing oxygen-rich blood to the major muscles.

• The muscles tense and become primed for action, which can cause trembling or shaking. Pulse rate and blood pressure go up. Extra oxygen is sent to the brain, increasing alertness — sight, hearing, and other senses become sharper.

• Anything unnecessary to survival is paused, which can cause physical responses:

  
  

  • Digestive system (upset stomach, dry mouth, or urgent need to use the bathroom)

  • Reproductive system (reduced interest in physical intimacy)

  • Circulatory changes (tingling, coldness, and/or sweating in the face, hands, and feet)

  
  

A Final Note on the Stress Response

The fight, flight, or freeze response is an important and natural way for the body to protect itself. But when it’s triggered by perceived — not actual — danger, the symptoms can feel intense and confusing. It’s important to understand that while these sensations can be deeply uncomfortable, they are not dangerous.

Your body is not broken. It’s doing exactly what it’s been designed to do: keep you alive. And with support, understanding, and the right tools (including therapy for anxiety or trauma), you can begin to feel safer in your body again — even when the alarm goes off.