The Power of PEM // Post-Exertional Malaise in ME/CFS

This week on Instagram, I shared a bit about post-exertional malaise (PEM), how it can be so unpredictable yet overwhelming. PEM is when symptoms are triggered 12-48 hours after you have done an activity. Now this activity can vary from person to person, and from day-to-day. What might trigger someone, someone else might manage fine.

Post-exertional malaise is often the defining symptom of ME/CFS, and The ME Association claimed that PEM is often “considered the hallmark characteristic of ME/CFS” yet, when I posted about it, so many people had never heard of it, or suffered with the symptom without knowing what it’s official name was.

This is why, I wanted to write a full blog post about it. This can be such a huge debilitating, horrific symptom of ME/CFS and it is clearly under-talked about and definitely underestimated.

Let me give you an example.

Amy, 24 years old and has had ME/CFS for 6 years goes shopping for a day. While out, she has lunch with a friend, stops for a drink in the afternoon and goes to the cinema. That night, she is a bit tired, and chooses to have an early night.

The next morning, she wakes up, feeling unrefreshed but still able to continue with her normal activities. She spends the morning doing some light cleaning and some work on her laptop. She’s feeling ok, not as good as yesterday but not awful.

Then comes the afternoon, she has some lunch, watches a film and falls asleep, inadvertently having a nap. She wakes up around 4, watches some more telly, has a tea and has another early night. This day might be considered a ‘rest day’ or a ‘lightly active’ day at most.

Amy wakes up the next morning and feels like she has been hit by a truck. The fatigue is overwhelming, the brain fog is taking over her mind like dark clouds on a rainy day, pain is spreading all over her body and she finds herself unable to move.

This is PEM. It is a delayed effect from the activities Amy carried out two days earlier. This isn’t a result from the cleaning the previous morning, it is a result from the activities she carried out the day before. Even despite the mostly restful day Amy had yesterday, she has still been struck with a crash.

This crash happened approximately 48 hours after the beginning of Amy’s active day, 36 days after the end of that day and about 24 hours after the beginning of her ‘rest’ day.

Amy thought she had had enough rest yesterday, she made sure to rest most of the afternoon, she even had a nap! How is the crash this bad? What could she have done differently?

Truthfully, nothing. Unless Amy had avoided the active day out, the crash, could not have been avoided.


This is the reality of life with ME/CFS. This is what PEM is. And this is why it is vital that we talk about this. That we start the conversation, we have the conversation with others who are suffering, with our friends and family to help them understand, even with strangers on the internet in order to raise awareness of this debilitating illness.

Now, let me make myself clear. The example I shared, is not an absolute reaction. Each person with ME/CFS will have different triggers, will have different reactions to different activities and will have a crash at different times after an activity.

One person may manage to do a 1 hour exercise class and escape a PEM crash but be triggered by a stressful 30 minute meeting on Zoom.

Another person may not be able to walk 10 steps without a severe crash for days, maybe weeks or months.

ME/CFS and PEM comes in many different forms, sufferers may be in many different stages and we all suffer in completely different ways. You can read more about this here.


If you have made it to the end of this post, I would love you to get involved and join the conversation.

I have started the hashtag on Instagram #PowerofPEM and I would LOVE it if you could get involved. All you need to do is share a photo of yourself, before and during post-exertional malaise, just like the one I shared this week, and talk about your experience with PEM. What are your triggers? How does it affect you? What do you find is the most common misconception about it?

I will be sharing the posts form everyone who gets involved and I want to thank you in advance for not only reading this post, but for taking the time to educate yourself, and others about this condition. Thank you for joining the conversation and for raising awareness.

Until next time,

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