Part 2 of 4 in the series When Stress Doesn’t Switch Off
This series looks at chronic stress through four clinical lenses: how to identify it, why the nervous system struggles to let it go, what it does to the body over time, and what can actually helps.
Part 1 – Is Your Body Stuck in Stress Mode?
Part 2 – Why Your Nervous System Stays on High Alert (you’re here)
Maybe you’ve noticed something doesn’t quite add up. By most measures, life is manageable. The job is okay. The relationships are okay. Nothing catastrophic is unfolding. And yet your body seems to have missed the memo. You’re tense. You’re tired. You’re scanning. You startle easily, sleep lightly, and find it hard to fully exhale — literally and figuratively.
If this sounds familiar, I want you to know something: this isn’t a character flaw, and it isn’t an overreaction. It’s biology doing exactly what it was designed to do. The problem is that it was designed for a different kind of world than most of us are living in.
The Stress Response Was Built for Emergencies
When you encounter something threatening — whether it’s a near-miss on the highway or a difficult conversation with your manager — your brain activates the hypothalamic-pituitary-adrenal (HPA) axis, triggering a cascade of hormones, primarily cortisol and adrenaline.¹ These aren’t bad hormones. In the right context, they’re remarkable: they sharpen attention, mobilise energy, suppress non-urgent functions like digestion, and prepare the body to respond.
The design assumes something important, though: that the threat will resolve. That there will be a return to baseline. That after the danger passes, the system will downregulate — cortisol will drop, heart rate will slow, and the body will have time to recover what it spent.
For acute, physical stressors — the kind humans have faced for most of our evolutionary history — this works beautifully. The problem is that we have a stress response designed for an era we no longer live in. Our nervous system has a difficult time distinguishing between a physical threat and a psychological one. Which means your body mounts essentially the same physiological response to a tense email as it does to a dangerous situation.² And psychological stressors rarely have a clear ending. The email thread continues. The worry doesn’t resolve. The demands don’t stop arriving.
The system is left running.
Why the Off Switch Stops Working
Under normal circumstances, the HPA axis is self-regulating. Cortisol itself signals the brain to slow production once the stressor has passed — a negative feedback loop that brings the system back to baseline.¹
But chronic activation gradually impairs this feedback. Prolonged exposure to elevated cortisol can reduce the sensitivity of the receptors responsible for shutting the response down, making it harder for the system to read its own signals.³ The result is a nervous system that has lost some of its ability to return to rest — not because anything is broken, but because the mechanism has been under sustained load without adequate recovery.
This is what makes chronic stress different from acute stress. It’s not just more of the same thing. The physiology changes.
The Nervous System Learns
There’s another layer to this that I think is important to understand, because it explains why some people seem to carry chronic activation even when their current life circumstances have genuinely improved.
The nervous system is, at its core, a prediction machine. It is constantly scanning the environment and comparing what it finds against a model built from past experience.⁴ When that model has been shaped by repeated or intense experiences of threat — a difficult period at work, a painful relationship, a childhood environment that required constant vigilance — the system learns to anticipate danger rather than wait for it. It stays primed.
This isn’t a malfunction. It’s the nervous system being efficient. If the world has reliably been demanding or unsafe, defaulting toward readiness is a sensible adaptation. The difficulty is that the pattern persists even when circumstances change, because updating a well-learned prediction requires repeated, accumulated evidence that things are different now. That takes time and — often — intention.
This is part of what trauma-informed therapeutic approaches work with. Techniques like EMDR (Eye Movement Desensitization and Reprocessing) aren’t about revisiting difficult memories for their own sake. At a neurological level, they help the nervous system reprocess experiences that have left it stuck in a pattern of anticipatory activation — updating the model, so the system can respond to what is actually present rather than what it learned to expect.⁵
This is slow, careful work, and it isn’t the right fit for everyone. But for people whose chronic activation has roots in past experience rather than current circumstances, it can be the missing piece.
When Worry Itself Becomes the Stressor
Even without a trauma history, the mind has a remarkable capacity to sustain the stress response through thought alone.
Research on what’s called perseverative cognition — the tendency to ruminate on past events or worry about future ones — shows that these mental habits drive the same physiological responses as real-time stressors.⁶ When you lie awake running through tomorrow’s difficult conversation, or replay a conflict from last week, your HPA axis responds as if the threat is present. Cortisol rises. Heart rate variability drops. The system activates.
This is why stress doesn’t reliably resolve when the external circumstances improve. The stressor becomes internal. The nervous system is responding to the contents of the mind, not just the events of the day. And the mind, for many of us, is not a quiet place.
Cognitive behaviour therapy (CBT) is a model designed to work with ones thoughts and the impact they have on the mind and body. CBT works at identifying and shifting mental loops that we get stuck in so that we can gain new insights and create alternate thought patterns to calm the active stress response.
What This Means
None of this is a verdict. It’s an explanation. A nervous system that has learned to stay activated — whether through accumulated daily stress, a period of prolonged difficulty, or the residue of earlier experience — is a nervous system that needed to adapt. Understanding that mechanism is genuinely useful, because it points toward what actually helps.
If you find yourself recognising the patterns described here — particularly the sense that your system stays activated regardless of what’s actually happening in your life — talking with a counsellor can be a meaningful part of understanding and shifting that. It doesn’t require a crisis to be worth exploring.
Shawna Bot is a Registered Clinical Counsellor at Acacia Health, practising at our Dockside Green location. She has specialized training in EMDR and works with individuals navigating trauma, relationship challenges, and the psychological dimensions of chronic stress. A complimentary 15-minute meet and greet is available to see if working together is a good fit. View Shawna’s full bio here.
- Chrousos GP. Stress and disorders of the stress system. Nat Rev Endocrinol. 2009;5(7):374–381. https://doi.org/10.1038/nrendo.2009.106
- McEwen BS, Gianaros PJ. Central role of the brain in stress and adaptation: links to socioeconomic status, health, and disease. Ann N Y Acad Sci. 2010;1186:190–222. https://doi.org/10.1111/j.1749-6632.2009.05331.x
- Sherin JE, Nemeroff CB. Post-traumatic stress disorder: the neurobiological impact of psychological trauma. Dialogues Clin Neurosci. 2011;13(3):263–278. https://doi.org/10.31887/DCNS.2011.13.2/jsherin
- Clark DA, Beck AT. Cognitive theory and therapy of anxiety and depression: convergence with neurobiological findings. Trends Cogn Sci. 2010;14(9):418–424. https://doi.org/10.1016/j.tics.2010.06.007
- Shapiro F. The role of eye movement desensitization and reprocessing (EMDR) therapy in medicine: addressing the psychological and physical symptoms stemming from adverse life experiences. Perm J. 2014;18(1):71–77. https://doi.org/10.7812/TPP/13-098
- Brosschot JF, Gerin W, Thayer JF. The perseverative cognition hypothesis: a review of worry, prolonged stress-related physiological activation, and health. J Psychosom Res. 2006;60(2):113–124. https://doi.org/10.1016/j.jpsychores.2005.06.074
