Post-Exertional Malaise (PEM) is something many of us with ME/CFS, Fibromyalgia, FND and Long COVID know all too well. That familiar crash after doing even the simplest of tasks—a walk around the block, a chat with a friend, or even just reading an interesting book. But what makes PEM so complicated is how it isn’t just physical exertion that triggers it. Mental and emotional stressors, overstimulation like bright lights or loud noises, and even poor diet can all cause PEM or make it much worse. This is where the nervous system steps into the spotlight.
What is PEM, and Why Does it Happen?
PEM is the body’s extreme response to activity or stress. When someone who suffers with PEM engages in activity—whether physical, mental, or emotional—their nervous system goes into overdrive. The body's normal ability to regulate stress, manage energy, and recover from exertion is severely compromised. As a result, a person can experience a delayed crash, often lasting days or even weeks.
But why does this happen? The nervous system plays a pivotal role in managing the body's responses to all kinds of stimuli. When the nervous system is already hypersensitive due to dysfunction, even low-level stressors are magnified. It’s as if the nervous system is constantly on high alert, responding to every little thing as though it were a major threat. This means that even small amounts of activity can lead to exhaustion, cognitive fog, and a flare-up of symptoms.
Stress Isn't Just Physical
One of the most perplexing aspects of PEM is figuring out what exactly triggered a crash. Sometimes, we expect to feel wiped out after physical exertion, but the severity of PEM can still catch us off guard. Even more confusing is when we experience a severe crash after only minor activity—or when we don’t crash as badly as we thought we would. Why is it that on one occasion, we manage okay, but the next time, even the same seemingly small activity leaves us struggling?
Imagine going for coffee with a friend. You laugh, chat, and feel great. Afterwards, you don't crash as badly and think, "Maybe I'm getting better!" But then confusion sets in when the next time you go for coffee, you crash severely. What's different this time?
The key lies in other stressors that might have been at play—stressors you didn't even notice. On the first occasion, you were relaxed, only dealing with the physical activity of going out, and your nervous system managed to cope. But on the second occasion, perhaps you were anxious about what to wear, worried about your appearance ("Do I look okay? Is my hair a mess?"), or stressed because a driver blocked you in on the way. Maybe you grabbed a quick meal high in sugar and carbs before meeting up. Each of these additional stressors compounds the load on your already overreactive nervous system.
The point here is that when you do something and enjoy it without additional stress, you may not crash as badly because you're only dealing with one primary stressor. Plus, when you're free from anxiety and truly enjoying yourself, feel-good hormones like dopamine kick in. Dopamine not only makes you feel more positive in the moment, but it can also help balance the nervous system, allowing it to cope better with the exertion. In these moments, your body and mind are working together, not just dealing with a physical challenge but supported by a mood boost. Do the same physical activity while you're worried or stressed, and it's double the load—or more. The nervous system perceives all these stressors cumulatively, leading to a more severe PEM.
PEM Can Be Triggered by Even the Simplest Tasks
It's important to acknowledge that, when severe, even basic tasks can trigger PEM. Taking a shower, preparing a meal, or sitting up for extended periods can all lead to a PEM crash. So, when we talk about going for a coffee, this may only be possible at a later stage in recovery when the nervous system has become less reactive. At earlier stages, the body may not tolerate anything beyond the most basic self-care activities, which can still be exhausting. PEM isn’t just reserved for big outings—it can be brought on by daily living tasks.
The Nervous System and the Accumulation Effect
Understanding that PEM results from multiple stressors is crucial. It’s not just physical exertion—mental and emotional stress, sensory overload, and even what we eat all pile on.
Take that coffee with your friend as an example. While it seemed like a harmless treat, even the coffee itself might have played a part in overstimulating your nervous system. Caffeine can increase alertness and energy, but for an already hypersensitive system, it could be just enough to push things into overdrive.
Then, if you had a meal full of sugar and carbs, your body now has to process that too, adding another burden on your system. Throw in loud noises, bright lights, or lingering worries on the way home, and suddenly you've got a perfect storm for PEM.
This accumulation of stressors is why managing these conditions is so challenging. Even if we carefully pace ourselves, other stressors—like overthinking, diet, or environmental stimuli—can sneak in and push us over the edge.
Remission, Relapse, and the Vicious Cycle
Many people with ME/CFS, Fibromyalgia, FND, or long COVID experience periods of remission. Symptoms ease, and it feels like recovery is within reach. Naturally, you start doing more activities, hoping to regain a sense of normalcy. But this often leads to overexertion and a relapse. The crash that follows is typically worse than the original symptoms, leading to a cycle of worsening PEM.
This cycle often triggers a cascade of stress: first the relapse, then anxiety over worsening symptoms, followed by poor sleep and heightened stress levels. All of this feeds back into the nervous system dysfunction, causing symptoms to spiral out of control. It's not just that we "did too much"—it's that the nervous system can't cope with the cumulative stress load, and it responds by shutting us down.
Managing PEM: The Nervous System at the Core
So, how can we manage PEM? The key lies in recognizing that the nervous system is central to everything. Here are some ways to support it:
Pacing: Learn to carefully ration your energy, even when you feel good. Doing less on good days can help avoid the crash on bad ones.
Managing Mental and Emotional Stress: Overthinking and emotional distress can trigger PEM just as easily as physical exertion. Practices like mindfulness, meditation, or talking to someone you trust can help lighten the emotional load.
Reducing Sensory Overload: Avoid overstimulation from bright lights, loud noises, and chaotic environments, which can all stress the nervous system.
Mindful Diet Choices: A diet low in sugar and inflammatory foods can support the nervous system by reducing the body's overall stress load.
Self-Compassion: Be gentle with yourself. Worrying about your appearance or overanalysing social interactions adds unnecessary stress. Accepting yourself as you are can alleviate some of the mental and emotional burdens.
Conclusion:
Understanding PEM means understanding how the nervous system works—and how fragile it can be when overstimulated. Recovery is a long and complex journey, but recognizing the nervous system's role in PEM is a crucial step in managing it. It's not just about limiting physical activity; it's about managing all forms of stress.
Take it slow, one step at a time. Remember, it's not about doing nothing—it's about doing the right things to protect your nervous system and avoid PEM. By being mindful of all the stressors in your life, you can better navigate the complexities of these conditions.
References:
Jason, L. A., & Zinn, M. (2019). Post-Exertional Malaise in ME/CFS: A Review. Frontiers in Neurology. Link to study
Nijs, J., & Meeus, M. (2014). Central sensitization in chronic fatigue syndrome and fibromyalgia: from pathophysiology to treatment. Clinical Rheumatology. Link to paper
Carruthers, B. M., & van de Sande, M. I. (2011). Myalgic Encephalomyelitis: International Consensus Criteria. Journal of Internal Medicine. Link to paper
Knoop, H., & Bleijenberg, G. (2010). Chronic fatigue syndrome: stress sensitization and cortisol regulation. Journal of Psychosomatic Research. Link to article
Holgate, S. T., Komaroff, A. L., Mangan, D., & Wessely, S. (2011). Chronic fatigue syndrome: understanding a complex illness. Nature Reviews Neuroscience. Link to paper
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