Why the Body Stays in Fight or Flight Long After the Danger Has Passed

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Your Health Magazine Contributor

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Why the Body Stays in Fight or Flight Long After the Danger Has Passed

Most people know the basic shape of the stress response. Something threatens you, your heart rate climbs, your breathing quickens, your muscles tighten, and your body readies itself to confront the threat or get away from it. Then the threat passes and things settle. That is how it is meant to work, and for the majority of stressful moments in a life, it does.

What is less widely understood is that the response does not always switch off. For some people, a nervous system that entered a protective state months or years ago never fully returned to baseline. They may describe themselves as always on edge, unable to relax, jumpy, exhausted, or braced for something they cannot name. They frequently understand exactly where the pattern came from. That understanding has not released it.

This article explains why.

What the fight-or-flight response does

The stress response begins in the brain. When the amygdala registers a threat, it signals the hypothalamus, which acts as a command centre for the autonomic nervous system. That system controls involuntary functions such as breathing, blood pressure, heart rate, and the constriction or dilation of blood vessels.

Harvard Health Publishing describes the two branches of the autonomic nervous system in terms of a car. The sympathetic branch functions like the gas pedal: it triggers the fight-or-flight response and provides a burst of energy to deal with perceived danger. The parasympathetic branch functions like the brake, promoting a “rest and digest” state that calms the body once the danger has passed.

The sequence is fast and coordinated. The adrenal glands release adrenaline, which raises heart rate and pushes blood toward the muscles. If the threat persists, a second system, the hypothalamic-pituitary-adrenal axis, keeps the body on alert through the release of cortisol. Harvard Health notes that this is a survival mechanism shared across mammals, and that it evolved to handle situations that were genuinely life-threatening.

Why it is supposed to switch off

Built into the design is an ending. Once the threat resolves, cortisol levels fall, the parasympathetic branch takes over, and the body returns to its ordinary state. In physiological terms, the stress response is meant to be a complete cycle: activation, action, and recovery.

That last phase matters. A body that has mobilised a great deal of energy needs to discharge it and then rest. In many everyday cases this happens without anyone noticing, because the stressor is small and the recovery is quick.

Some approaches to trauma treat this cycle as central. Somatic Experiencing, developed by Peter Levine, is built on the premise that post-traumatic stress symptoms are an expression of stress activation and an incomplete defensive reaction to a traumatic event, as described in the first randomised controlled trial of the method, published in the Journal of Traumatic Stress in 2017. On this view, the problem is not the activation itself but the fact that it was never allowed to finish.

What happens when it does not complete

There are several ways a stress response can fail to complete. The threat may have been prolonged rather than brief, so there was no clear moment at which it ended. The person may have been unable to fight or flee, as is common in childhood, in accidents, or in situations where escape was impossible. Or the danger may have recurred often enough that the system learned to stay ready.

When any of these happen, the body can remain partially mobilised. Harvard Health describes what follows: chronic low-level stress keeps the HPA axis activated, “much like a motor that is idling too high for too long,” and persistent adrenaline surges can damage blood vessels and raise blood pressure.

The neuroscientist Bruce McEwen gave this a name. He called the cumulative wear on the body from repeated or sustained stress “allostatic load.” Writing in the Annals of the New York Academy of Sciences in 2004, McEwen described how the same systems that protect the body in the short term cause damage when activated over long periods, contributing to impaired immunity, atherosclerosis, obesity, bone demineralisation, and atrophy of nerve cells in the brain.

How a protective state becomes a baseline

The word baseline is doing important work here. A nervous system that stays activated long enough does not experience itself as activated. It recalibrates. What was once an emergency setting becomes the ordinary one, and calm begins to feel unfamiliar or even unsafe.

Research on post-traumatic stress disorder shows what this looks like in the brain. A review by Shin, Rauch and Pitman, also published in the Annals of the New York Academy of Sciences, in 2006, found heightened amygdala responsivity in people with PTSD, not only when confronted with reminders of trauma but during the processing of emotional information unrelated to it. The same review examined altered function in the medial prefrontal cortex and hippocampus, regions involved in regulating fear and placing memories in context.

In practical terms, the alarm system has become more sensitive while the systems that would ordinarily tell it to stand down have become less effective. The person is not choosing to react. Their threat-detection system is firing at a lower threshold than it used to.

Why understanding does not resolve it

This is the part that frustrates people most. They have done the work of understanding. They can explain the origin of their reactions, often in detail. And their body carries on as though none of that explanation had taken place.

The reason is that the stress response is not run by the parts of the brain that understand. The amygdala and the autonomic nervous system operate below conscious thought and faster than it. Insight is processed in the cortex; the alarm is processed elsewhere. You can know, accurately and completely, that you are safe, and the amygdala can nonetheless continue to signal that you are not. Knowledge and physiology are running on different tracks.

This does not make understanding worthless. It provides context, reduces self-blame, and helps a person make sense of what is happening. But it addresses the story of the pattern rather than the pattern itself. A nervous system that has learned to stay activated has to be shown, through experience rather than explanation, that it can stand down.

What approaches address it

Several approaches exist, from established cognitive therapies to body-based approaches to trauma, and they work in different ways.

The American Psychological Association’s clinical practice guideline for PTSD gives its strongest recommendations to cognitive processing therapy, prolonged exposure therapy, and trauma-focused cognitive behavioural therapy, with eye movement desensitisation and reprocessing among the interventions it also suggests. These are the treatments with the largest body of controlled-trial evidence, and for many people they are effective.

Body-focused methods take a different route, working through physical sensation and the gradual completion of stress responses rather than primarily through thought. The evidence base is smaller and more recent. The 2017 trial of Somatic Experiencing mentioned above, involving 63 participants with PTSD, found significant reductions in post-traumatic symptoms and depression compared with a waitlist group, and its authors noted that further research is needed to understand who benefits most. Methods of this kind are increasingly offered alongside, rather than instead of, conventional treatment.

Alongside formal treatment, Harvard Health describes relaxation techniques that counter the stress response directly by engaging the parasympathetic branch. These do not resolve an entrenched pattern on their own, but they give the body repeated experiences of standing down, which is precisely what a chronically activated system lacks.

No single approach suits everyone. What matters is that the approach chosen reaches the level at which the pattern is held.

When to see a doctor

Several of the symptoms described here overlap with medical conditions, and that overlap should not be dismissed. Mayo Clinic lists heart disease, thyroid problems such as hyperthyroidism, respiratory disorders, chronic pain, and the side effects of certain medications among the medical problems that can produce anxiety-like symptoms, and notes that in some cases these symptoms are the first sign of a physical illness.

A racing heart, persistent restlessness, trouble sleeping, or unexplained physical tension warrant a medical evaluation before they are attributed to stress. Nothing in this article replaces that. If a doctor has ruled out a physical cause and the pattern persists, the mechanisms above may help explain why, and may point toward the kind of help most likely to reach it.

Author bio

Yana Depsames is a Certified Regression Therapist trained through the Regression Academy, and a member of the EARTh Association and the Spiritual Regression Therapy Association. She runs One With Prana, a regression therapy and somatic trauma healing practice in Fort Collins, Colorado, and works with clients online. Her work is complementary to, and not a replacement for, licensed clinical care.