You may know this feeling: your stomach tightens, a stinging sensation in your abdomen, your pulse quickens and your heart beats harder, your palms get sweaty, your breathing becomes shallow, and on top of it all – dizziness, weakness, or even the sensation of fainting. All of this is part of what is called a sympathetic response of our nervous system – or more simply: a stress response.
What connects our body, a stress response, and an emotion like anxiety is what we will take a closer look at in the following.
Our Nervous System – A Brief Overview
The brain and spinal cord together form the central nervous system. Everything that leaves the spinal cord, runs through the body, and comes back in on the other side belongs to the peripheral nervous system – our body’s nervous system. This system carries several synonymous names: vegetative, autonomic, or sympathetic nervous system. Vegetative, because among other things it controls digestion. Autonomic, because it works automatically, beyond our conscious control. Sympathetic – not because it has anything to do with sympathy (a misleading name) – but because the nerve that mobilises energy in the body is called the “Sympathicus.” More precisely, it is not a single nerve but a system of many nerve fibres and nerve clusters (ganglia) – hence its full name: systema nervosum sympatheticum, the sympathetic nervous system.
The purpose of this system: to enable us to deal with stressors – and even threats – and to overcome them.
The Sympathetic Nervous System – The Gas Pedal
The sympathetic nervous system is the network of nerve fibres and clusters responsible for activation and resource mobilisation. When it fires, the body revs up – accompanied by symptoms like a racing heart, sweating, rapid and shallow breathing, trembling, or dizziness.
The sympathetic system knows only one direction from the factory: forward. It works like the gas pedal in a car – and it only ever floors it. When activated, all systems are brought up to full operating temperature. It knows nothing else.
The Parasympathetic Nervous System – Taking Your Foot off the Gas
The autonomic nervous system does not consist of the sympathetic alone. It also has an authority that brings the system back down, slows it, and returns it to rest: the parasympathetic nervous system.
“Para” comes from the Greek and means something like “beside” or “next to.” The parasympathetic system owes its name to its anatomical position: its nerve fibres originate in the brain and in the lower spinal cord – functionally and anatomically alongside the sympathetic system.
The function of the parasympathetic system? The inhibition of the sympathetic. Physical calming, then, does not mean pressing the gas and the brake at the same time – it means taking your foot off the gas.
A particularly important nerve of the parasympathetic system is the vagus nerve (Latin: nervus vagus). It is the largest parasympathetic nerve and runs from the brainstem through the entire trunk down to the abdominal cavity, supplying the heart, lungs, larynx, and the organs of the digestive tract.
Crucial for understanding anxiety and stress responses is that the vagus nerve does not originate from a single source. It arises from two different nuclei in the brainstem: the ventral vagal complex (from the nucleus ambiguus) and the dorsal vagal complex (from the dorsal motor nucleus). These two branches are evolutionarily different in age and serve fundamentally different functions – a distinction that will become important shortly.
In summary: we have an autonomic nervous system consisting of the sympathetic (activation) and the parasympathetic (inhibition). The largest parasympathetic nerve is the vagus nerve, whose two branches – ventral and dorsal – play different roles in how we process stress.
The Polyvagal Theory According to Stephen Porges
A Built-In Alarm System
Stephen Porges coined the term neuroception for our nervous system’s ability to constantly scan our environment, our inner experience, and our understanding of the external world – always searching for signs of danger, threat, or stressors. This happens entirely unconsciously and is not part of deliberate behavioural control. It is more of an evolutionary feature than a malfunction.
Three Protective Mechanisms of the Nervous System
Polyvagal Theory distinguishes three different coping or operating modes of our nervous system. Imagine a potential threat is detected – what happens now?
Mode 1: The Social Safety Network (Social Engagement)
This mode is controlled via the ventral pathway of the vagus nerve and is almost exclusively limited to mammals – in humans, it is particularly well developed. This network operates through safety and connection: we try to connect with other people nearby and to receive support.
In this state, we can articulate our thoughts clearly, think in structured ways, plan, and act. We feel relatively calm. The body can digest, rest, sleep, and learn. Mental and cognitive functions work reliably. We can remember, process emotions, have access to ourselves, and are receptive. We perceive ourselves, are capable of empathy, consideration, and patience.
Mode 2: Mobilisation (Sympathetic – Fight or Flight)
If the attempt to connect with others has not led to a reduction in the perceived threat, the second mode engages: the mobilisation system.
From the perspective of our nervous system, which is interested in our survival, the worst case has now arrived – the threat has reached our immediate living space and we must respond. The directive is simple: provide energy, redistribute everything else. Like a nation switching to a war economy. What the body needs to survive the threat is energy – and everything that is not essential for survival is dropped.
Concretely, this means: the activated sympathetic system promotes the release of stress hormones into the blood – adrenaline (small, fast, short-lived) and cortisol (large, bulky, long-lived; approximately 90 minutes to return to baseline) from the adrenal glands. These hormones produce far-reaching changes at the biological and physiological level:
- Energy reserves are mobilised. Lipolysis (fat breakdown) and glycogenolysis (breakdown of sugar reserves) are accelerated – the reserves built up during calmer times are now consumed.
- Breathing becomes short and shallow (hyperventilation) to enrich the blood with oxygen needed for the imminent energy expenditure.
- Blood is redistributed, flowing primarily into the largest muscle groups – legs, back, chest. This is why we get cold hands and feet.
- Pain relief and protection: The organs preemptively release endogenous opiates for pain relief, as well as anti-inflammatory substances and clotting factors into the blood.
- The prefrontal cortex is dialled down. The activity of thinking, planning, and deciding is throttled. Behaviour is now primarily guided by evolutionarily older brain structures – fast, reflexive, but without the fine control of conscious thought.
- Perception changes: Vision narrows, memory is undermined, tunnel vision sets in.
In this mode, we fight or we flee. Every negotiation, every connection has been of no use. This response is also known as the fight-or-flight response.
Mode 3: Shutdown – Collapse (Dorsal Vagus)
If even the mobilisation of all resources – fight or flight – has led to no change, Polyvagal Theory identifies a third mode: the so-called shutdown or collapse.
This mode is controlled via the dorsal pathway of the vagus nerve and represents humanity’s evolutionary inheritance – a remnant from the time when we were still animals. It controls our oldest survival instinct: the playing-dead reflex.
Activation of the shutdown network leads to a rapid decrease in muscle tone, low blood pressure and pulse, slow and shallow breathing, as well as dissociation, emotional numbness, apathy, and listlessness. An animal plays dead while in the clutches of a predator – ready, at the right moment, to shift back into activation and flee.
The Interplay
From Polyvagal Theory, we can identify three layered protective mechanisms through which our nervous system responds to threats:
- Safety and social engagement – seeking connection, staying regulated
- Mobilisation – providing energy for defence or flight
- Collapse – conserving resources until the right moment
The Window of Tolerance According to Dan Siegel
Dan Siegel complements the biological perspective of Polyvagal Theory with a psychological lens. He proposes a window of tolerance for arousal – a range within which we are capable of regulation.
The idea behind it: if you want to regulate, you need a functioning foundation to actually use the skills required for it – thinking, feeling, self-access, calm, decision-making capacity, motor control. If that foundation is missing, you cannot apply the methods that would bring about regulation.
In Dan Siegel’s model, when we look at physical arousal, there are three zones: a zone of too much arousal (hyperarousal), a zone of too little arousal (hypoarousal) – and in between, a window where there is just enough arousal to remain functional.
Both models connect well:
- Within the window of tolerance, we are in ventral vagal activation – in the safety network of social engagement. We can think, feel, connect.
- Above the window of tolerance, in hyperarousal, we are in sympathetic activation – the mobilisation of energy. Racing heart, tension, fight or flight.
- Below the window of tolerance, in hypoarousal, we are in the dorsal vagal response – collapse. Shutdown, dissociation, apathy, emotional numbness.
How Anxiety Can Reinforce Itself
Psychosomatics describes the connection between psyche (mind) and soma (body): both interact with each other. One conditions the other – and vice versa.
This also applies to our psychological defence and protection mechanisms against threat and danger. When I notice an elevated pulse, sweaty palms, and a tense alertness within me, it sharpens my antennae: I focus more on negative, unclear, or mismatched information in my surroundings. If I then notice a negative facial expression – one that may well have been there before but escaped my attention – it confirms my body’s reaction. Another layer is added, the mobilisation of energy intensifies. The cycle begins again: scan – reaction – re-scan.
And here comes a decisive point: through learning processes and conditioning, the threshold of what is perceived as threatening can shift – without anything in the external world having objectively changed.
How does this work? Through classical conditioning, originally neutral stimuli – a particular place, a smell, a situation – become linked to the anxiety response. The body has learned: there was danger here. And the next time, the system responds to the stimulus alone, before any real threat is even present.
Through stimulus generalisation, this response spreads to increasingly similar situations. What was once the narrow lift cabin becomes the narrow room, then the full bus, then the crowd. The window of tolerance narrows, the threshold for activation drops – and anxiety gains ground, not because the world has become more dangerous, but because the nervous system has shifted its calibration.
Peter Levine and Somatic Experiencing Therapy
The theory of Somatic Experiencing builds on our understanding of arousal and activation in the body – and takes it one step further. The starting point: our nervous system fundamentally works well as it is. It has found ways to deal with the stress of its environment.
Peter Levine looked into the animal kingdom and noticed something striking: prey animals – antelopes, for example – are exposed to life-threatening stress on a daily basis. Yet they do not develop post-traumatic stress disorder. Why not?
If you observe an antelope that has just escaped death, you see involuntary twitching and trembling. Wild and chaotic. After a few minutes it stops, the antelope walks on, goes about its business – and everything seems to be fine.
As we know from Polyvagal Theory, we move through different nervous system states: from connection to mobilisation to collapse. The playing-dead reflex – our evolutionary inheritance. The antelope seems to shake itself vigorously after playing dead, almost as if it needs to pass back through the mobilisation phase on its way to rest – the phase that could not be discharged through playing dead.
Humans typically do not do this. They suppress, inhibit, and store the physical activation that accompanied the stressor. This way, it can remain bound in the body for years and generate tension.
The idea behind Somatic Experiencing therapy: physical arousal that arose from a stressor or trauma and was not discharged remains stored in the body. This creates tension – chronic, often unconscious. In therapeutic work, these frozen physiological activation states can be slowly and gradually thawed, allowing them to discharge gently and in a controlled manner. Not through overwhelm, but through careful approach.
What Does This Mean for You?
We do not need to be traumatised to make use of the insights anchored in Polyvagal Theory, the Window of Tolerance, and Somatic Experiencing research.
The message is fundamentally simple: the trembling, the shallow breathing, the sweating – all of what we notice when anxiety arrives and the body is stressed – is part of a protective mechanism that has existed for millennia. The body is not working against us, but for us. The symptom is not the problem. The problem arises when we suppress the symptom. The body knows what it is doing – it has been doing this for millions of years.
We can support it by learning not to push away the reactions and states that arise, but to endure them – and to give them the space they need to fulfil their purpose and subside.
If you recognise yourself in these descriptions and feel that anxiety or stress responses are taking up more space in your daily life than you would like, that is a good starting point for a conversation. Psychological counselling can help you understand your nervous system better, widen your window of tolerance, and find a healthier way of relating to what your body is telling you.