Why it's important that PEM is not fatigue

I've heard from a few people recently that, when they pointed out to a healthcare practitioner (HCP) that PEM* is not fatigue, the HCP felt that they were just being pedantic. It seems many HCPs believe that, even if there is a difference between PEM and fatigue, the difference is just a matter of terminology and detail, not a matter or any real-world significance.

So here's why PEM is different from fatigue, and why this difference is important, put very simply.

PEM includes a long list of symptoms. Fatigue is just one of these symptoms. Some others include: tinnitus, headaches, GI problems, light and noise sensitivity, musculoskeletal pain, muscle weakness, cognitive dysfunction, dizziness and flu-like symptoms. Some of these symptoms are much more debilitating and unpleasant than mere fatigue.

But there is an even more important difference between PEM and fatigue: duration.

Fatigue generally lasts 24 hours. In really exceptional circumstances, say if someone ran a marathon, fatigue might last a couple of days.

Healthcare practitioners know that if they do something that causes fatigue, the consequences won't last for more than a day or two. If a physiotherapist gives their patient a bit too much exercise to do and the patient becomes too fatigued, it isn't really a problem; the patient is only fatigued for a day, the physio adjusts the exercise plan, and life goes on. Fatigue isn't dangerous.

PEM is dangerous. PEM can last hours, days, weeks, months, or a lifetime. Its duration and severity are wildly out of proportion to whatever prompted it. It can result in permanent harm. PEM can take a person who is able to work or look after their children, and make them bedbound. PEM destroys lives.

Any healthcare practitioner who fails to recognise the difference between fatigue and PEM is a danger to their patients.

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*PEM is post-exertional malaise, also known as post-exertional symptom exacerbation. It is a symptom of ME/CFS and is also found in many people with long Covid.