While trauma is a word used to describe a range of dysfunctional individual or collective experiences, it is normally defined in two distinct categories – single-shock trauma, whereby an individual experiences a sudden and immense threat to survival; or developmental trauma, whereby the physiological development of the child is impaired by a distorted perception of self and other.

To more fully understand trauma and its physiological causes, we must understand something of the human nervous system. In human beings the Autonomic Nervous System, part of the Peripheral Nervous System that operates in addition to the Central Nervous System, is responsible for regulating physiological response to the environment. The ANS is split into two parts as are our emotional selves – the sympathetic nervous system (sym pathos meaning literally ‘with feeling’) manages ‘going up’ expressive energies such as anger, fear, joy and excitement that involve movement towards or away from an object; while the parasympathetic system manages ‘going down’ emotions of yielding and collapse such as shame, guilt, despair, contentment and satisfaction that saturate the subjective physiological state of the body system. What is important to note is that these two systems work in tandem – the ‘going up’ SNS expresses and releases intense affect while the ‘going down’ PrNS permeates the body with it and there is a cohabitation and often a conflict between the two.

Crucially in regards to trauma and dissociation, the ANS is also responsible for triggering the body’s physiological response to threat and danger. Both sides of the ANS are able to respond and depending on the individual conditioning and the extremity of the situation depends on what side gets activated. In tolerable situations, where the individual can internally manage the immense fear and anxiety, the sympathetic system will trigger and utilize a fight or flight response as adrenaline is released and the body becomes charged for action. This allows for immediate expression.

The PrNS, however, operates by immobilization, which can manifest as freezing or fainting. This is when the system completely shuts down as a behavioural response to threats that are perceived to be inescapable. This immobilization happens when the right cortex of the brain becomes overwhelmed as a result of stimulus that cannot be contained or effectively processed, and the left dampens regulatory processing by preventing it from accessing conscious awareness. These would be because more powerful affects, such as terror, horror or rage are coursing through the physiological system. Peter Levine uses the example of an impala being chased by a cheetah to demonstrate the freeze reflex. As the cheetah pounces, through instinct the impala has entered an altered state of consciousness and surrendered to its impending death. The system has effectively ‘inhibited’ or blocked the extreme affect it is experiencing because it is too intense. This is an ‘interrupted impulse’, whereby the vaso-motoric cycle towards expression, discharge and relaxation has not been completed and the re-balancing of the SNS and PrNS systems cannot take place.

Working with the effects of trauma in the therapy room can often require a two-fold approach, one focusing on the sensory motor triggers, utilising techniques such as Eye Movement Desensitisation Reprocessing, with the other focusing on the issues surrounding the developmental deficits that have left the affect regulatory system compromised in its ability to deal with and process traumatic experience.

PTSD

Post-Traumatic Stress Disorder (PTSD) is a complex psychophysiological condition that arises following exposure to events that overwhelm an individual’s capacity to cope, integrate experience, and restore internal regulation. It is not simply a disorder of memory or cognition, but a disturbance of the entire organism—affecting perception, emotion, physiology, identity, and relational functioning.

PTSD develops after exposure to actual or threatened death, serious injury, or violation, whether experienced directly, witnessed, or, in some cases, repeatedly encountered in professional contexts. What distinguishes PTSD from ordinary stress responses is not the intensity of the event alone, but the individual’s inability to complete the physiological and emotional response to threat.

PTSD is not a failure of resilience, nor merely a psychological condition, but a disruption of the organism’s innate capacity to regulate, integrate, and recover from threat. Its roots lie in incomplete physiological responses, inhibited affect, and compromised regulation—often shaped by early developmental experience. Effective treatment respects this complexity, working simultaneously with body, mind, and relationship to restore flexibility, safety, and meaning.

Clinically, PTSD is characterised by four core symptom clusters:

  1. Intrusion – involuntary re-experiencing of the traumatic event through flashbacks, nightmares, somatic memories, and intrusive images.

  2. Avoidance – efforts to evade reminders of the trauma, whether external (people, places, situations) or internal (thoughts, emotions, bodily sensations).

  3. Negative alterations in cognition and mood – persistent shame, guilt, emotional numbing, alienation from others, and a distorted sense of self or world.

  4. Hyperarousal and reactivity – heightened startle response, hypervigilance, sleep disturbance, irritability, and chronic anxiety.

At its core, PTSD reflects a nervous system that continues to respond as if danger is present, even when safety has been restored.

Causes and Risk Factors

Traumatic Exposure

PTSD can arise from a wide range of experiences, including combat, sexual or physical assault, childhood abuse or neglect, accidents, medical trauma, natural disasters, or sudden loss. However, not all traumatic exposure results in PTSD. Two individuals may experience the same event with vastly different outcomes.

Developmental Vulnerability

A significant risk factor for PTSD is early developmental trauma. Chronic misattunement, neglect, or abuse during childhood disrupts the maturation of affect regulation, leaving the nervous system less capable of tolerating and integrating intense arousal later in life. As a result, individuals with developmental trauma are more vulnerable to PTSD following single-incident trauma.

Perceived Inescapability

Events perceived as inescapable—where fight or flight is impossible—are particularly likely to result in PTSD. In such situations, immobilisation responses dominate, increasing the likelihood of dissociation and incomplete processing.

Lack of Social Support

The absence of relational support following trauma significantly increases PTSD risk. Safe interpersonal contact plays a crucial role in restoring nervous system regulation and meaning-making.

Physiological Understanding of PTSD

PTSD is fundamentally a disorder of autonomic regulation. The autonomic nervous system (ANS), which governs physiological responses to threat, becomes chronically dysregulated following trauma.

  • Sympathetic dominance leads to persistent hyperarousal: anxiety, vigilance, agitation, and rage.

  • Parasympathetic dominance, particularly via immobilisation pathways, results in shutdown states: emotional numbing, dissociation, collapse, and depression.

Rather than fluidly oscillating between activation and rest, the nervous system becomes rigidly organised around survival.

Fight, Flight, Freeze, and Collapse

During trauma, the organism mobilises energy for survival. When fight or flight cannot be executed or completed, the system may default to freeze or collapse. In PTSD, these responses are not resolved. The body remains primed for threat, repeatedly re-activating survival responses in response to reminders that may be symbolic, sensory, or relational.

Memory and Brain Function

Traumatic memories are encoded differently from ordinary autobiographical memory:

  • The amygdala becomes hyper-responsive, detecting threat even in ambiguous stimuli.

  • The hippocampus, responsible for contextualising memory in time and space, is often inhibited, resulting in fragmented, timeless memory.

  • The prefrontal cortex, which mediates reflection and regulation, shows reduced activation during trauma recall.

As a result, traumatic memories are experienced as present-moment events rather than past experiences, accompanied by the original physiological state.

Dissociation and Inhibited Affect

When affect exceeds tolerable limits, conscious awareness may be inhibited. Dissociation protects the individual during trauma but becomes pathological when it persists. The unintegrated affect remains stored in the body and is re-evoked through physiological pathways rather than narrative recall.

Therapeutic Treatment of PTSD

Effective treatment must address both the physiological and psychological dimensions of trauma. Insight alone is insufficient; regulation and integration are central.

Stabilisation and Safety

The first phase of treatment focuses on restoring a sense of safety and enhancing regulatory capacity. This may include:

  • Psychoeducation about trauma and the nervous system

  • Grounding techniques

  • Development of internal and external resources

  • Strengthening relational safety within the therapeutic alliance

Without sufficient stabilisation, trauma processing can be retraumatising.

Bottom-Up Interventions

Because PTSD is primarily stored in subcortical and physiological systems, bottom-up approaches are essential:

  • EMDR (Eye Movement Desensitisation and Reprocessing) facilitates the integration of traumatic memory by engaging bilateral stimulation while maintaining dual awareness.

  • Somatic therapies (e.g., Somatic Experiencing) focus on completing interrupted defensive responses and restoring autonomic flexibility.

  • Sensorimotor psychotherapy works directly with posture, movement, and bodily sensation to renegotiate trauma responses.

These approaches aim to discharge trapped survival energy and restore nervous system balance.

Top-Down Approaches

Cognitive and relational work helps contextualise and integrate experience:

  • Trauma-focused CBT addresses distorted beliefs and avoidance patterns.

  • Narrative integration allows traumatic memory to be placed in temporal context.

  • Relational and attachment-based therapies address shame, identity disturbance, and interpersonal patterns rooted in developmental trauma.

Integration and Meaning

Later phases of treatment focus on integration—developing a coherent sense of self that includes but is not defined by trauma. This may involve grief work, identity reconstruction, and renewed engagement with life and relationships.

International Trauma Support Resources

UK Trauma Support Resources

  • NHS (National Health Service) – Access to trauma-focused therapies via GP referral, including PTSD services.
  • Mind – UK mental health charity offering information, helplines, and local trauma support.
  • Samaritans – 24/7 emotional support for people in distress or experiencing trauma. Phone: 116 123.
  • Rethink Mental Illness – Support, advice, and services for trauma and related mental health challenges.
  • PTSD UK – Charity dedicated to raising awareness of PTSD and supporting those affected.