What Is the “Fight-or-Flight” Response? How Anxiety and Stress Show Up in the Body—Not Just the Mind

Anxiety and stress can show up in many ways: racing thoughts, difficulty concentrating, or trouble sleeping. But it’s not just a mental experience—anxiety often manifests physically in the body. To better understand how our bodies respond to anxiety, it’s important to learn how various systems and organs work together when we encounter threats or stressors.

What Triggers an Anxiety Response?

The nervous system becomes activated when we perceive a threat. This triggers the fight-or-flight response—our body’s natural reaction to danger or stress, whether the threat is physical or emotional. In today’s world, perceived threats can range from serious danger to everyday stressors like arguments, missed deadlines, or running late.

When this response is activated, the brain’s amygdala—our fear center—sends a distress signal to the hypothalamus, which then activates the autonomic nervous system (ANS). The ANS controls involuntary functions like breathing, heart rate, and digestion. It has two main branches:

• The sympathetic nervous system (SNS): activates the fight-or-flight response.
• The parasympathetic nervous system (PNS): promotes rest and recovery (often called the “rest and digest” system).

During fight-or-flight, the SNS kicks in, stimulating the adrenal glands to release stress hormones like adrenaline and cortisol. These hormones can cause physical symptoms such as increased heart rate, muscle tension, and a redirection of blood flow away from the digestive system toward the muscles. While these responses are meant to keep us safe, chronic activation of the SNS over time can negatively impact our health and well-being.

What Happens When the Nervous System Stays Activated Too Long?

Prolonged fight-or-flight states can lead to a continuous release of stress hormones, which may:

• Raise blood pressure
• Disrupt digestion
• Contribute to headaches, fatigue, or muscle tension
• Cause changes in appetite
• Create hormone balance
• Weaken the immune system

Over time, chronic activation can also affect mental health, increasing the risk for anxiety, depression, and irritability. Since our body’s systems are deeply interconnected, understanding how each one contributes to the stress response is key to developing tools that support nervous system flexibility—the ability to shift between states of activation and calm.

While the SNS plays an important role in survival, it's equally important to help the body transition out of this high-alert state and activate the PNS to restore balance.

The Role of the Parasympathetic Nervous System (PNS) and Why Flexibility Matters

When the PNS is active, muscle tension decreases, and heart rate and breathing slow down. Digestion resumes, and the body can conserve energy and begin to recover. This state supports both physical and emotional healing.

Having nervous system flexibility—the ability to move smoothly between activation (SNS) and rest (PNS)—is crucial. Although excessive time in a heightened state of stress can be harmful, the SNS is necessary for responding to real danger. The key is to restore balance afterward.

As we deepen our understanding of the mind-body connection, it becomes increasingly clear how chronic stress impacts our physical health. Practices that activate the parasympathetic nervous system—such as somatic movement, breathwork, and grounding exercises—can help bring the body back into a calm and regulated state.

Bringing awareness to what triggers your stress response allows you to be more intentional about using tools that promote regulation. Start by tuning in to your body: notice areas where you hold tension (like the neck or shoulders) and incorporate light stretching to release it. Techniques like box breathing, diaphragmatic breathing, yoga, or walking in nature can also help activate your parasympathetic system and bring you back to a state of rest.

It’s not always easy to recognize our physical or emotional triggers. Talking with a counselor about your experiences with anxiety and stress can provide a supportive space to explore what’s going on in your body and learn practical tools for building nervous system flexibility. Over time, this can reduce anxiety and improve your overall well-being.

To learn more about how counseling can help you manage stress and anxiety or to schedule an appointment, reach out to us here.

-By Emily Weber, LMSW