I have spent the better part of my life in a complicated relationship with my own nervous system. I spent years living with complex PTSD and an equally long journey learning how the nervous system works, employing every tool available to me, top-down and bottom-up, cognitive and somatic, ancient and clinical to help me heal, grow and be here today. To offer this work. To provide this substack. To be a yogi. To refine hands-on work in our classrooms.

This essay, the final one in this foundational series, is the one that matters most to me personally, because it’s not only where science meets yoga philosophy, but it’s where both intersect with my own lived story. If you’ve read everything that came before this, thank you. This is what it was building toward.

Because here’s the question underneath all of it: why learn anything about the nervous system?

And here’s my answer: because it’s at the heart of everything. It’s at the heart of why yoga works. The avenue through which Patanjali was trying to guide us all along, long before humanity had words for it. And the answer for how we face the single greatest challenge in every single human being’s life: stress.

Here’s the thing about stress: we’ve all been sold a lie.

Not intentionally, maybe. But somewhere along the way, “stress” became a dirty word — something to eliminate, avoid, manage into oblivion. We talk about it the way we talk about a diagnosis. Something wrong. Something to fix.

But stress isn’t inherently bad. And yes, I just said that as someone who once had complex PTSD. If anyone had reason to write stress off entirely, it might be me. And I still won’t, because this is too important to collapse into something simple.

Some stress is not only good for you, it’s necessary for growth, resilience, and a well-regulated nervous system. And in fact, stress can be the very thing that teaches us compassion and lends us wisdom. The problem isn’t stress itself. The problem is where you land on the stress continuum, and whether your nervous system has the capacity to return to baseline after the experience. We’ve been pointing to this all along: to train nervous system flexibility, to have resilience, is to train both branches of the autonomic nervous system. That includes the sympathetic branch.

Let me walk you through the full spectrum of what we term “stress.”

The Stress Continuum

Think of stress not as a single thing but as a range, a long line stretching from mildly challenging all the way to traumatic. Where any given experience lands on that continuum depends on a lot of factors: intensity, duration, frequency, context, and perhaps most importantly, your nervous system’s current capacity to process and recover; it’s flexibility.

At one end, you have stress that builds you. At the other end, you have stress that breaks something open that doesn’t close back up on its own. Most of us live somewhere in the middle, moving up and down the line depending on the day, the season, the decade.

Understanding where you are, and where your students are, changes how you work with bodies. It changes how you teach. It changes how you live.

Eustress: The Good Stuff

Eustress is the term coined by endocrinologist Hans Selye in the 1970s to describe stress that is positive, motivating, and within our capacity to handle. The prefix eu- comes from Greek, meaning “good” or “well.”

Eustress is the flutter before a performance. The focused tension of a deadline you actually care about. The physical challenge of a hard yoga class. The nervousness before a first date or a public talk. It’s the stress that sharpens you.

Physiologically, eustress activates the sympathetic nervous system, heart rate increases, attention narrows, energy mobilizes, but in a way that feels enlivening rather than threatening. And critically, once the stressor passes, the system returns to baseline without much trouble.

Eustress is associated with improved performance, increased motivation, a sense of meaning, and can enhance immune function. It involves a stressor, but it feeds you.

Hormetic Stress: The Dose Makes the Medicine

Hormesis takes this a step further. Hormetic stress refers to a biological phenomenon in which a low-to-moderate dose of a stressor produces an adaptive, strengthening response, even when higher doses of the same stressor would be harmful.

Cold plunges are a great modern example. Immersing yourself in cold water is a stressor. Your body doesn’t love it at first. Your sympathetic nervous system fires hard, cortisol spikes, your breath goes ragged — maybe you instantly pee yourself like I always did! But with repeated, controlled exposure, your system adapts. You get better at tolerating and recovering from cold.

That’s the point of hormetic stress. It trains your stress response. With repeated exposure you recover faster, regulate more efficiently, and become more flexible, both in your nervous system and in your response to the stressor itself.

Exercise is hormetic stress. Fasting can be hormetic stress. Heat exposure, certain plant compounds, intermittent breath holds, all hormetic. The principle is consistent: the body, given the right dose of challenge with adequate recovery, adapts.

This is not a metaphor. It’s physiology. And what hormetic stress specifically trains is resilience, resilience in the nervous system, the body, and the mind. That’s not a side effect. That’s the mechanism and the foundation of autonomic flexibility. Which brings us directly to what building that resilience actually looks like over time.

Widening the Window

There’s a concept I want to name here because it’s central to everything: the window of tolerance. Developed by psychiatrist Daniel Siegel, it describes the zone of nervous system arousal — or stress — within which a person can function, process experience, and remain regulated. Not numb, not flooded, present and capable.

What hormetic stress and eustress do, over time, is widen that window.

Every time you take the cold plunge and come back to baseline, you’ve practiced the full arc: activation, peak, recovery. Every time you move through a hard yoga class and soften at the end, your nervous system files that experience. I went there and came back. The window expands. What used to throw you off now barely registers. What used to flood you now just gets your attention.

This is stress resilience, essentially your ability to be flexible to stressors and have the capacity to recover. You build resilience the same way you build physical strength: by showing up to appropriate challenges, recovering well, and repeating. At its heart, this is toning both branches of the nervous system, the sympathetic to activate at the capacity needed for the challenge, and the parasympathetic to allow you to adequately recover. Widening the window isn’t about becoming numb to stress. It’s about becoming more flexible to it.

When Stress Exceeds Capacity: Trauma

Here’s where the continuum shifts.

When a stressor exceeds the nervous system’s current capacity to process and integrate, whether because of its intensity, its duration, its unpredictability, or the absence of support and safety, the system doesn’t complete its natural arc. It gets temporarily stuck.

This is trauma. Not a character flaw. Not weakness. A nervous system response to an experience that was simply too much, too fast, too long, or too alone.

Trauma isn’t defined by the event itself. Two people can go through the same experience and have profoundly different responses based on their history, their window of tolerance, their access to co-regulation, and a dozen other factors. What traumatizes one person may barely register for another, and that doesn’t make either person wrong. It makes us human, with different nervous systems shaped by different lives.

What’s worth distinguishing is what trauma can look like when the system has what it needs to move through it. When the stressor hits and the system is pushed hard, very hard, what follows is a natural, healthy response: grief, rage, fear, shock, or some combination of usually very intense emotions. The nervous system fires at full capacity. That acute response can last hours, days, sometimes a couple of weeks. But given enough time, enough safety, and enough support, it can run its course. The system metabolizes what happened and files it alongside other significant life events as a learning lesson. One the system can return to as perhaps greater caution, but not as something unresolved. Not stuck. That’s one generalized example of trauma completing its arc. The system metabolizing what it was given.

This is not the same as the event not mattering. It mattered. Your nervous system learned something from it. But phobias didn’t form, relationships weren’t fractured over the long term, and your health wasn’t chronically impacted. The experience was real and difficult, and the system did what it was designed to do: respond, process, and recover.

PTSD and CPTSD: When Trauma Becomes a Condition

It’s worth naming clearly: experiencing trauma does not mean a person has PTSD. PTSD is a clinical condition that can develop in the aftermath of trauma when the nervous system cannot fully complete that arc of metabolization. When the experience was simply too much, too fast, too long, or too alone for the system to integrate at the time, it gets stuck.

Post-Traumatic Stress Disorder develops when the nervous system remains dysregulated long after the threat has passed. And here is what “stuck” can look like over time: what began as an acute startle response, a natural alarm that fired when it needed to, doesn’t resolve. It becomes adaptive. The nervous system, trying to protect the person from future threat, reorganizes itself around that unmetabolized experience. Hypervigilance sets in, along with numbness or dissociation, shame, and a startle response that won’t settle. Intrusive memories, nightmares, avoidance, emotional reactivity — these are the nervous system’s continued attempts to process something it couldn’t fully metabolize in the moment. And over time, these adaptations can stop being just symptoms and start shaping life globally: relationships can fracture, social engagement might narrow, work can suffer, and physical health may be impacted in ways that can feel entirely disconnected from the original event.

Complex PTSD is related but distinct. Where PTSD often follows a single event or a defined period of trauma, CPTSD is associated with prolonged, repeated trauma, particularly when it occurred in a context of captivity or powerlessness: childhood abuse, domestic violence, chronic neglect, prolonged medical trauma. CPTSD carries all the hallmarks of PTSD but adds layers of profound difficulty with self-concept, emotional regulation, and relationship, because the trauma wasn’t just what happened. It was the ongoing environment in which the person had to survive and, by extension, had to adapt who they were to get through it. The coping strategies, relational patterns, and beliefs about self that formed during that period were genuine survival responses. The painful part is that they don’t simply switch off when the environment does.

Both conditions represent a nervous system that got stuck at the far end of the continuum. And while only a small percentage of people receive a formal diagnosis, diagnosis doesn’t equate to prevalence. Not everyone has access to a provider. Not everyone seeks help. Diagnosed or not, individuals with these conditioned nervous systems will end up in your classroom, whether it’s a Trauma-Informed Yoga class or not. They are there.

Which is why tactful consent is paramount to a safe classroom environment. And why fostering agency and upholding student autonomy is exactly what supports these individuals.

I know this firsthand. I was the student who would walk into yoga class and lay in savasana the entire class. That would drive most yoga teachers hell-bent on “controlling space,” ahem, I mean “holding space,” simply mad. But why did I do it? Because the vibes, my teacher’s presence and voice, even the other students’ energy, the atmosphere itself, was so calming. But my poor CPTSD-conditioned nervous system simply couldn’t muster the effort to move through any other pose than savasana. So I laid there, healing by osmosis from the collective yoga vibes. That was me exercising my agency. And my teacher respecting my autonomy. Agency: the choice. Autonomy: the freedom to exercise it.

Whether you know it or not, these students are in your classroom. Support them, with clear consent and respect for their agency and autonomy.

When the Poison Becomes the Medicine

There is something that lives on the other side of the hardest end of the continuum that doesn’t get talked about enough. Not because it isn’t real, but because you can only see it from the other side, and not everyone makes it there.

It’s called Post-Traumatic Growth, a term coined by psychologists Richard Tedeschi and Lawrence Calhoun in the 1990s to describe the positive psychological change that can emerge from the struggle with deeply challenging, even devastating life experiences. Not in spite of the trauma. But because of the reckoning with it.

I want to be careful here, because PTG is not a guarantee, it’s not a silver lining to be prescribed, and it is absolutely not a reason to minimize what someone has been through. A friend of mine was recently diagnosed with PTSD and had never once heard of Post-Traumatic Growth. When I told her it existed, something shifted in her face. Not relief exactly, but possibility. That’s what I want to offer here: not a promise, but a door worth knowing about.

Because here’s what I’ve lived: I cannot say I’m grateful for what happened to me. If I could wave a wand and make sure those experiences never occurred, I would do it without hesitation. But that’s not possible. And when you arrive at the end of that road, when every other option has been exhausted, what remains is acceptance. Not resignation. Not pretending it was okay. Pure, unadulterated acceptance of the ugly things you endured.

And when that acceptance comes, something fundamental shifts. It doesn’t reverse the identity reformation that happened in survival mode. What it introduces instead is an incomparable compassion. Compassion steeped in a complete absence of judgment, for yourself and for others, because you have lived inside the darkest mechanics of being human and came out the other side knowing exactly how someone ends up there.

You also gain wisdom. Lessons about yourself and about humanity that, from where I stand, no other experience could have taught you. It’s almost like your window gets utterly shattered. Just shards and pieces left of yourself, if you truly reach that far end of the continuum. But as you work your way back, as you pick up those pieces, put them together, and heal what you have access to, you build a wider window than you ever had before.

That is Post-Traumatic Growth.

Why This Matters in a Yoga Context

The student who goes rigid when you approach. The student who cries in savasana without knowing why. The student who pushes past their edge every single class and can’t seem to stop. The student who dissociates in deep hip openers. The student who, when you provide them an assist, sighs like they haven’t breathed in years. These and countless other representations of nervous systems expressing their position within the continuum abound in every classroom.

Every nervous system is on the continuum. And so is yours.

But here’s the thing: you’re a yoga teacher, you work with nervous systems. Full stop. Every cue, every playlist, every hands-on assist lands somewhere on this continuum for the person receiving it.

And here’s what’s worth sitting with: yoga, in its fullness, is one of the most sophisticated nervous system tools humanity has ever developed. Not because it was designed in a laboratory, but because across thousands of years of practice and observation, it arrived at the same destination science is only now catching up to. Asana moves the body through activation and release, training the full arc of the stress response. Breathwork directly modulates the autonomic nervous system, shifting state from the inside out. Mantra, drishti, music, and class structure shape the environment of safety that determines whether a nervous system can regulate or not. Meditation and silence ask the student to simply be present with themselves, building the top-down awareness that makes regulation possible off the mat. And consensual hands-on teaching, offered with skill and respect for student autonomy, provides a quality of co-regulation that might be difficult to access through verbal cueing alone.

All of it, every tool in the yoga teacher’s hands, is in the business of widening the window.

Understanding this doesn’t make you a therapist. It makes you a more informed teacher, one who knows that the body is always doing something intelligent, that stress isn’t the enemy, and that the ancient practice you’re holding is doing something far more profound than improving flexibility. It is, when offered well, supporting the single greatest challenge every human being faces.

This is not peripheral to yoga. This is the center of it.

Stress Is a Teacher

The goal is not a stress-free life. A stress-free life is a stagnant one.

The goal is a nervous system that can meet challenge, move through it, and return home to itself. A nervous system with enough resilience and flexibility that the inevitable stressors of being alive don’t shatter you. They shape you. And sometimes, as we’ve explored, they may shatter you first, but what gets rebuilt ends up wider and wiser than what existed before.

Few yoga sages lived within our chaotic, demanding, often disembodied world. They lived within curated environments adapted for introspection, meditation, and less stimulation, so that samadhi, enlightenment, can emerge. We modern yogis get to learn how to do that outside those ideal conditions. And yet we challenge ourselves with the same staggering goal, on a modern path sprinkled with unpredictable, hidden landmines — what our nervous systems perceive as stressors — one after another, often without warning.

In spite of the landmines, when we shift our perspective towards finding liberation, ananda, we can get there faster. We see that it’s a journey supported, and sometimes hindered, by the resiliency of our nervous system rather than our capacity for 108 sun salutations or our ability to do a handstand. This reframing allows us to genuinely internalize what Patanjali meant by abhyasa and vairagya. Not as a daily inversion practice or enduring a grueling vinyasa series with poise, but as dedicated practice toward non-reaction. In modern, scientific terms: widening our window of tolerance.

This is what Patanjali was always pointing at. Not perfection of posture. Not the performance of calm. But the training of our nervous systems to be resilient enough to meet the full spectrum of being alive. And to move ourselves back, with as much grace as we can muster, from anywhere we find ourselves on the continuum.

To be on the yogic path is to be on a journey to train the nervous system to widen its window. To have the capacity — through the exhilaration of eustress, the intentional training of hormetic stress, and even the navigation of all the more challenging points further along the spectrum — to bring ourselves back toward regulation. And when we can’t, when life deals us a landmine that leaves us stuck at one end, as it did mine, then our ultimate yogic lesson has begun. That of compassion.

Because what is it to be a yogi, truly, if not to hold searing compassion — for others, yes, but starting first with ourselves.

This is the ninth and final essay in the foundational series on nervous system literacy for yoga teachers. If you’re just finding this work, start from the beginning with The Autonomic Nervous System: Your Invisible Co-Teacher, or subscribe to follow along as we move into new territory from here.

Join me in Bali next month, August 15-29, 2026 as we explore the nervous system and so much more within the lush jungle backdrop of Selemadeg. The Samasthala 200HR YTT explores the full range of yoga concepts and presents Rubber Band Method® assists as a complimentary teaching tool in any class. Book today and save £500 or $650!!

The Stress Continuum: Why Stress Isn’t the…