Post-Exertional Malaise (PEM) is a delayed worsening of symptoms following physical, cognitive, or emotional exertion. But it’s more than just feeling tired—it’s a sign that the nervous system is struggling to process and recover from stress.
Unlike typical exhaustion, PEM doesn’t always strike immediately. You might feel fine after an activity, only to crash hours or even days later. That’s because PEM isn’t just about “energy depletion”—it’s a dysfunctional response to stress that sets off a cascade of nervous system dysregulation, immune activation, and metabolic shifts.
Even minor activities, like taking a shower or having a conversation, can trigger a significant worsening of symptoms. If PEM were purely about physical strain—such as an oxygen deficit or mitochondrial dysfunction, as many suggest—we would expect it to occur primarily with high levels of exertion. But that’s not what happens.
The fact that even the lightest activity can lead to a crash suggests that PEM is more about how the nervous system is reacting to a perceived threat. Exertion itself may not be the problem—it’s how the body processes and responds to it.
Why Graded Exercise Therapy (GET) Fails
After being diagnosed with ME/CFS, Long COVID, or FND, many of us are told that graded exercise therapy (GET) will help us recover. The idea behind GET is that by gradually increasing physical activity, we will rebuild stamina and regain function. But for those with PEM, this approach often causes harm.
Why? Because our nervous system sees exercise as stress. When we attempt structured exercise, it reinforces the stress response. Instead of building resilience, we experience more symptoms: inflammation, neurological dysfunction, pain, and extreme fatigue. The cycle repeats. The principle of “neurons that fire together wire together” applies here—each time we try and crash, we strengthen the negative association between movement and stress.
When I was told graded exercise would help me recover, I was confused—because any form of exercise made me worse. Even the physical effort of taking a shower would worsen symptoms. And I used to exercise all the time—yet I still got sick! Against my better judgment, I listened to the doctors and physiotherapists, assuming they knew what they were talking about. So, I followed a graded exercise plan.
This turned out to be the biggest mistake I ever made. Instead of helping, it reinforced the stress, caused me to regress, and left me in a worse state than before—triggering severe neurological and physiological symptoms.
This left me with a nervous system that became extremely reactive—not just to exercise but even to simple movements. Retraining it has been a long and difficult process, and I’m still battling with it. But I’ve come a long way from where I was because I took the time to study how the nervous system works and figured out what my body actually needed to heal.
Many of us who suffer the most severe PEM from exercise were highly active before illness. Athletes, fitness enthusiasts, or anyone who regularly pushed their physical limits seem to be more prone to this cycle. When you frequently push past exhaustion, your body is constantly triggering a stress response. Over time, this rewires the nervous system, reinforcing the idea that exertion equals danger.
Not convinced? Well, we know that cognitive, emotional, environmental, and even nutritional stressors also trigger PEM and cause the same crash. You’ve probably experienced this yourself. It’s the same neural pathways involved. The reality is that when the nervous system reacts poorly to a perceived stressor—in this case, exercise—it’s what triggers PEM.
The Alternative: Rewiring the Nervous System’s Response to Exercise
The key isn’t to avoid movement altogether—it’s to rewire the system so that physical activity no longer triggers a stress response. This happens when movement is associated with safety and enjoyment rather than strain and danger.
So, how do we achieve that? The answer lies in how the brain responds to different types of experiences. When an activity feels fun, rewarding, and genuinely enjoyable, the nervous system reacts very differently compared to when movement feels forced, stressful, or exhausting.
When you’re simply focusing on the physical strain or stress of an activity, the body releases cortisol, adrenaline, and other stress hormones, activating the sympathetic nervous system—the “fight or flight” response. This can leave you feeling drained, overwhelmed, and susceptible to PEM. Additionally, physically strenuous activity forces the body into a heightened state of alertness, reinforcing the cycle of stress and post-exertional crashes.
But when you engage in activities that genuinely excite and fulfil you, your brain releases feel-good neurotransmitters like dopamine and serotonin. These chemicals regulate the nervous system, shifting you out of a stress-induced state and into a more balanced one.
Dopamine, often called the “reward chemical,” reinforces positive behaviours by creating feelings of satisfaction and motivation. GABA (gamma-aminobutyric acid), an inhibitory neurotransmitter, calms the nervous system and counteracts the excitability of stress responses. Together, they activate the parasympathetic nervous system—the “rest and digest” state—which reduces stress and promotes relaxation and recovery.
This is why fun, light, and flow-based activities are often the best approach. They don’t just distract the mind; they prevent the nervous system from perceiving movement as a threat in the first place. The more you experience activities that bring you joy and excitement, the more you train your nervous system to associate movement with safety rather than danger.
The best way to do this? Engage in activities that feel safe, fun, and rewarding. Finding an activity that genuinely excites you, and ideally doing it with a friend, can reinforce feelings of safety and connection, further calming the nervous system.
For me, that’s surfing. Of course, I wasn’t able to just jump straight into it. It took time to find a way to combine fun with movement in a way that didn’t trigger my symptoms. Getting in the water was a great start—whether it was swimming or simply enjoying the moment, it helped me reconnect without pushing myself too far.
Taking the paddleboard out, having fun with friends—it was all about movement that felt natural and enjoyable. The key was finding ways to incorporate exercise without it feeling like a chore or a challenge.
It’s actually much harder than it sounds to truly experience joy in the moment—this isn’t something that can be forced or faked. Joy is an autonomic physiological response, and for that to happen, your body must feel genuinely safe and at ease.
When you experience true joy, that’s when real change starts to happen. The more you engage in movement that feels safe and enjoyable, the more you begin to rewire your nervous system’s response to exercise. Over time, this creates a positive feedback loop—turning movement from something that once felt overwhelming into something that feels freeing.
Recovery Takes Time
This process isn’t instant. Teaching your nervous system that movement is safe again requires patience, not force. But by starting with small, enjoyable activities, you can begin to shift your body’s response. Over time, movement stops being a trigger and starts becoming a tool for recovery.
The key isn’t to ‘push through’ discomfort—it’s to find ways to move that feel good, safe, and sustainable. That’s where real healing begins.
The Bigger Picture
Bringing joy into movement doesn’t just make exercise easier—it changes the way your nervous system perceives it. When movement feels safe and enjoyable, your body begins to unlearn its fear response, reducing the stress that fuels PEM.
Recovery isn’t about doing more. It’s about working with your body, not against it. By focusing on safety, enjoyment, and gradual progress, you can rebuild trust with your nervous system—and with time, movement can become freeing again.
References
What Fires Together, Wires Together:Netzley, M. (2021). What Fires Together, Wires Together. Medium. Retrieved from https://michaelnetzley.medium.com/what-fires-together-wires-together-163fa2e62d8d
The Cortisol Creep: Sweeney, M. (2019). The Cortisol Creep: How Stress Can Build Up Without You Realizing It. Healthline. Retrieved from https://www.healthline.com/health/fitness/the-cortisol-creep
Flow Sports: A Natural Therapy for Your Nervous System: FND Health. (2021). Flow Sports: A Natural Therapy for Your Nervous System. FND Health. Retrieved from https://www.fndhealth.com/post/flow-sports-a-natural-therapy-for-your-nervous-
PMC5573220:Toga, A. W., & Thompson, P. M. (2017). Brain Mapping: A Practical Guide. PubMed Central. Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC5573220/
How the Nervous System Controls Your Reality: Huberman Lab. (2022). How the Nervous System Controls Your Reality. YouTube. Retrieved from https://www.youtube.com/watch?v=h0jbiabEIkg
Effects of Exercise Training on the Autonomic Nervous System with a Focus on Anti-Inflammatory and Antioxidant Effects: Author Unknown. (2021). PubMed Central. Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC8868289/
