AUTHOR: 
AERYN O'HALLORAN

Mind–body practitioner and educator specializing in nervous system regulation and chronic illness.

DATE: 
DECEMBER 19, 2025

Trauma and the Nervous System: 

A Physiological Definition

Trauma and the Nervous System: 

A Physiological Definition

This article defines trauma in physiological terms rather than psychological ones. Some of the concepts may feel abstract at first because they describe processes that happen beneath conscious thought. You don’t need a background in neuroscience or trauma theory to read this. If the explanations resonate more than they make immediate sense, that’s normal, and often a sign that the framework is describing lived bodily experience.

A NOTE FOR READERS

In somatic and neurophysiological frameworks, trauma is defined less by the presence of an event and more by its effect on nervous system regulation. When experiences exceed the nervous system’s ability to respond and recover, protective survival responses may remain active, leading to ongoing patterns of autonomic dysregulation. This article presents a physiological definition of trauma grounded in survival-related nervous system function and examines how trauma-related states show up in the body. By framing trauma as a regulatory process rather than a psychological construct, this perspective helps explain persistent somatic symptoms, the limits of insight alone, and the overlap between trauma physiology, chronic illness, and autonomic conditions.



ABSTRACT

Trauma is often described in terms of events: what happened, when it happened, and how it is remembered. In somatic and neurophysiological models, however, trauma is defined less by the event itself and more by how the nervous system reorganizes in response to overwhelming demand.

From this perspective, trauma is not primarily psychological. It is a functional state of the nervous system, characterized by persistent alterations in regulation that influence physiology, perception, and behavior long after the original threat has passed.

This definition helps explain why trauma-related symptoms often appear in the body, why they are resistant to insight alone, and why individuals with chronic illness may experience trauma-like nervous system patterns even without a clearly defined traumatic event.








Introduction

Somatic trauma models conceptualize trauma as the result of incomplete physiological resolution rather than exposure alone. When the nervous system is unable to fully mobilize, discharge, and settle following threat, protective responses may remain active beyond their useful window.

A key distinction in these models is that trauma does not arise simply from exposure to stress or danger, but from incomplete physiological recovery. 
















This flexibility supports physiological stability across changing conditions. 

When sensory modulation capacity is reduced, the system becomes less discriminating. Sensory input that would typically be tolerated may instead trigger defensive autonomic responses, while recovery from stimulation becomes slower and less reliable.







Somatic trauma models conceptualize trauma as the result of incomplete physiological resolution rather than exposure alone. When the nervous system is unable to fully mobilize, discharge, and settle following threat, protective responses may remain active beyond their useful window.

A key distinction in these models is that trauma does not arise simply from exposure to stress or danger, but from incomplete physiological recovery. 






Trauma as Incomplete Physiological Resolution

Trauma-related patterns are shaped by interconnected survival systems responsible for threat detection, arousal, and defensive action. These systems evolved to prioritize speed and protection and operate largely outside conscious awareness.

When these networks remain persistently activated or inhibited, the result is not only emotional distress, but ongoing physiological dysregulation. This may affect heart rate and blood pressure, breathing patterns, digestion, immune signaling, pain processing, sleep, and energy levels.

These patterns reflect nervous systems that adapted to sustained demand rather than returning to baseline once the threat resolved.
















From an autonomic standpoint, this reflects reduced flexibility between sympathetic activation and parasympathetic recovery.

Rather than transitioning smoothly between alertness and rest (activation and recovery), the nervous system may remain biased toward sustained sympathetic dominance (e.g., tachycardia, hypervigilance, insomnia) or toward compensatory hypoarousal (e.g., exhaustion, shutdown, dissociation).

These are not transient emotional states. They are state-dependent physiological patterns that shape symptom expression across multiple systems.







Trauma-related patterns are shaped by interconnected survival systems responsible for threat detection, arousal, and defensive action. These systems evolved to prioritize speed and protection and operate largely outside conscious awareness.

When these networks remain persistently activated or inhibited, the result is not only emotional distress, but ongoing physiological dysregulation. This may affect heart rate and blood pressure, breathing patterns, digestion, immune signaling, pain processing, sleep, and energy levels.

These patterns reflect nervous systems that adapted to sustained demand rather than returning to baseline once the threat resolved.





Core Response Networks and Nervous system regulatlion

One of the most clinically relevant contributions of somatic trauma theory is its shift away from event-based definitions of trauma.

From a nervous system perspective, trauma can arise not only from acute, life-threatening experiences, but also from:

⋆ prolonged illness or injury
⋆ repeated medical interventions (e.g., surgeries)
⋆ certain dental procedures
⋆ chronic stress without adequate recovery
⋆ sustained uncertainty or lack of safety
⋆ cumulative physiological overload

In these contexts, the nervous system may never complete defensive responses or reestablish baseline regulation. Over time, survival patterns become fixed.

This distinction is particularly relevant in chronic illness populations, where trauma-related nervous system dysfunction often emerges without an event that meets conventional trauma criteria.









Trauma Beyond Events

Rather than presenting primarily as explicit memory, trauma-related nervous system patterns often manifest as autonomic dysregulation.

Common expressions include:

⋆ persistent sympathetic activation 
⋆ oscillation between high arousal and collapse 
⋆ impaired vagal tone and reduced regulatory flexibility 
⋆ heightened interoceptive sensitivity 
⋆ difficulty tolerating stimulation or stress

These responses are not voluntary and are not maintained by conscious thought. They reflect state-dependent physiology shaped by the nervous system’s attempts to maintain safety under what it perceives as ongoing threat.







Created by SM Ronyfrom Noun Project
Created by SM Ronyfrom Noun Project
Created by SM Ronyfrom Noun Project
Created by SM Ronyfrom Noun Project

Autonomic Dysregulation as a Trauma Expression

Rather than presenting primarily as explicit memory, trauma-related nervous system patterns often manifest as autonomic dysregulation.

Common expressions include:

⋆ persistent sympathetic activation 
⋆ oscillation between high arousal and collapse 
⋆ impaired vagal tone and reduced regulatory flexibility
⋆ heightened interoceptive sensitivity 
⋆ difficulty tolerating stimulation or stress

These patterns are not voluntary and are not maintained by conscious thought. They reflect state-dependent physiology, shaped by the nervous system’s attempts to maintain survival under conditions it perceives as ongoing threat.








periods of sustained sympathetic activation—such as elevated heart rate, heightened vigilance, rapid breathing, and increased metabolic demand—followed by depletion, shutdown, or prolonged loss of biological energy

Created by SM Ronyfrom Noun Project

Autonomic Dysregulation as a Trauma Expression

Rather than presenting primarily as explicit memory, trauma-related nervous system patterns often manifest as autonomic dysregulation.

Common expressions include:

⋆ persistent sympathetic activation 
⋆ oscillation between high arousal and collapse 
⋆ impaired vagal tone and reduced regulatory flexibility 
⋆ heightened interoceptive sensitivity 
⋆ difficulty tolerating stimulation or stress

These patterns are not voluntary and are not maintained by conscious thought. They reflect state-dependent physiology, shaped by the nervous system’s attempts to maintain survival under conditions it perceives as ongoing threat.








a decreased ability of the nervous system to settle, adapt, and return to baseline after stress, injury, or illness.

Created by SM Ronyfrom Noun Project

Autonomic Dysregulation as a Trauma Expression

Rather than presenting primarily as explicit memory, trauma-related nervous system patterns often manifest as autonomic dysregulation.

Common expressions include:

⋆ persistent sympathetic activation
⋆ oscillation between high arousal and collapse 
⋆ impaired vagal tone and reduced regulatory flexibility 
⋆ heightened interoceptive sensitivity 
⋆ difficulty tolerating stimulation or stress

These patterns are not voluntary and are not maintained by conscious thought. They reflect state-dependent physiology, shaped by the nervous system’s attempts to maintain survival under conditions it perceives as ongoing threat.








increased awareness of internal bodily sensations such as heart rate, pain, nausea, dizziness, or breath

Created by SM Ronyfrom Noun Project

Autonomic Dysregulation as a Trauma Expression

Rather than presenting primarily as explicit memory, trauma-related nervous system patterns often manifest as autonomic dysregulation.

Common expressions include:

⋆ persistent sympathetic activation
⋆ oscillation between high arousal and collapse 
⋆ impaired vagal tone and reduced regulatory flexibility 
⋆ heightened interoceptive sensitivity 
⋆ difficulty tolerating stimulation or stress

These patterns are not voluntary and are not maintained by conscious thought. They reflect state-dependent physiology, shaped by the nervous system’s attempts to maintain survival under conditions it perceives as ongoing threat.








sustained mobilization of cardiovascular, respiratory, and attentional systems in response to perceived threat or demand

Created by SM Ronyfrom Noun Project

Autonomic Dysregulation as a Trauma Expression

In people with chronic illness, trauma-related nervous system patterns often overlap with post-infectious, inflammatory, or autonomic conditions.

Symptoms such as fatigue, pain amplification, digestive disturbance, immune reactivity, and cognitive difficulty may be influenced not only by the underlying condition, but by a nervous system that remains organized around protection rather than recovery.

This does not suggest that chronic illness is caused by trauma. Rather, it highlights that nervous system state plays a role in how symptoms are expressed, tolerated, and resolved, regardless of the originating factor.







Trauma, Chronic Illness, and the Body

This interaction between trauma physiology and sensory input is explored further in my article, Sensory Modulation and the Nervous System, where regulatory capacity is examined through the lens of sensory processing and autonomic load.










Because trauma-related patterns are shaped by parts of the nervous system that operate outside conscious awareness, they are often not accessible through reasoning, insight, or reframing alone.

This helps explain why people may understand their symptoms intellectually, recognize that they are safe, engage in therapy or education, and yet continue to experience pronounced physiological reactions.

Somatic trauma models do not reject cognitive approaches. They recognize that regulation often needs to come first. Changes in nervous system state often need to occur before cognitive interventions can take hold.












Why Cognitive Approaches Alone Are Often Insufficient for trauma treatment

When trauma is understood as a pattern of nervous system organization rather than a historical event, the focus shifts.

Instead of asking only what happened, attention turns toward how the nervous system adapted, which survival patterns remain active, and what conditions support a return to flexibility and recovery.

This perspective frames symptoms not as personal failure or psychological weakness, but as adaptive physiology that may require different inputs in order to change.












Implications for Understanding Nervous System Regulation

Defining trauma as a nervous system process has practical implications.

For clinicians, it provides a way to understand symptoms that do not respond to standard interventions, explains variability and relapse without blaming the individual, and supports approaches that address regulation alongside pathology.

For individuals, it offers an explanation that matches lived experience, does not pathologize the individual, reduces self-blame, and clarifies why healing often requires physiological support rather than effort or willpower.








Why This Definition Matters Clinically

The framework presented here reflects an integration of peer-reviewed research, cross-disciplinary theory, and clinical observation. While sensory modulation is a well-established concept within occupational therapy and mental health literature, its application to chronic illness, post-viral syndromes, and autonomic dysregulation remains limited in mainstream medical models.

The interpretations offered are informed by existing literature, observations drawn from my work with a limited but consistent demographic, and my own lived experience navigating chronic illness and recovery. This work is not intended to replace medical diagnosis or treatment, but to contribute a regulatory lens that may help contextualize persistent, multisystem symptoms where conventional explanatory frameworks are insufficient.










Author’s Note on Scope and Interpretation

Levine, P. A., et al. (2015). Trauma and stress-related disorders: A neurobiological perspective. Frontiers in Behavioral Neuroscience.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4316402/

van der Kolk, B. A. (2014). The body keeps the score: Brain, mind, and body in the healing of trauma. Viking.











REFERENCES

" The fact that I saw change so quickly proves that the right help, the right first step, the right process makes all the difference..."

— KELLY M

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— JAMIE R

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" I was able to accomplish all my errands and when I got home at the end of the day, I didn’t crash. That’s the first time that’s happened in years! "

"I have ups and downs in my life in general, but I am stronger now."

"I finally feel I understand exactly what I need to do to start healing my dysregulated nervous system"

"I'm back to my normal self but even better than before!"

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