WTF is PEM?!

Explaining PEM (Post-Exertional Malaise) to those who’ve never experienced can be daunting. It’s not just tiredness or fatigue—it’s a total betrayal of your body, a system meltdown that turns even everyday tasks into risky ventures.

This severe condition, the defining feature of ME/CFS and many Long COVID cases, is a significant life-destroying effect that we must urgently address. Part of addressing it is more public awareness, so please keep reading and we’ll do our best to help you understand!

PEM 101

  • Post: It happens after you’ve done something, but of course, it’s not so simple; we’re talking hours, but usually, days after the activity that triggered it, it can hit 24-96 hours later, and it’s cumulative!

  • Exertional: It’s not just exercise. Exertion can be anything—walking too fast, sitting upright for too long, thinking too hard, or even feeling emotions too intensely.

  • Malaise: A medical term for “feeling horrible.” With PEM, multiply the horrible by a billion, people often describe it as being hungover, having the flu with all its awful symptoms and being poisoned simultaneously.

PEM stands for Post-Exertional Malaise, but some prefer to call it PESE (Post-Exertional Symptom Exacerbation) or PENE (Post-Exertional Neuroimmune Exhaustion). It’s not just “feeling bad” after doing too much—it’s a full-blown escalation of symptoms that can last for hours, days, weeks, months or even indefinitely. PEM is the term most widely used, so we’ll stick with it here.

What does it actually mean? Let’s break it down.

One syndrome, endless hellish possibilities:

Just like most diseases, ME/CFS & Long COVID have huge spectrums, and how they impact each individual is slightly different. Some people who are only very mildly affected can hold down their jobs and live almost regular lives, but intense cardio exercise, like running, skipping, jumping, etc., would be off-limits.

PEM can last days to months or even trigger an indefinite baseline decrease if the energy exertion is way beyond the individual’s limit; this limit is often called an “energy envelope.” Trying to remain within that energy limitation is called pacing, and pacing is a cruel form of energy management that people have no choice but to practice, thanks to the lack of medical treatment.

Pacing requires unbelievable levels of discipline, even for milder people. Imagine you’re about to miss your tram and want to sprint, but suddenly, you must remind yourself that you can’t—and that’s a mild example!

Why you can’t just “push through” PEM

You might ask yourself, well, those symptoms sound awful, but why not just “push through” the PEM and get yourself closer to living a normal life that isn’t defined by energy limits? Surely one can push through “fatigue”?? That way, you don’t need to spend the day in bed resting after going to a concert or just making it to a doctor's appointment the day prior.

We wish! Pushing through PEM is dangerous because PEM builds up; you can’t force yourself to move through the pain, palpitations, dizziness, fevers, etc., as someone with another disease might. Instead of passing, the crash will worsen, and repeating this process puts someone at high risk of a lower baseline with even more limitations.

Here’s a snapshot of what PEM feels like:

“It’s like I caught the flu, but my limbs are made of lead, and my brain feels like it’s on fire.”

“I feel like my energy has been unplugged, and my body’s in free fall. It’s terrifying.”

“Muscle pain so intense that even a blanket hurts. And the tinnitus? Louder than my thoughts.”

“I wake up feeling off, my eyes feel starved of oxygen, there’s a feeling of disorientation. Trying to focus hurts, my head hurts, my energy is lower and feeding myself is an accomplishment.”

How PEM escalates with severity

Notice the range of symptoms described? If the disease is on the worse side of the spectrum, so are the limitations and boundaries:

  • Very mild: Cardio exercise and intense, packed schedules tend to be off-limits.

  • Mild: Walking too fast, standing for hours at a time, or leaving home for more than one day in a row might trigger it.

  • Moderate: Walking down a flight of stairs, sitting upright for hours, or being outside with unfamiliar sensory input can cause crashes.

  • Severe: Even walking slowly to the bathroom, screen time longer than a few hours a day, or talking to a carer for too long might trigger PEM.

  • Very severe: Most exertion is off-limits other than the absolute minimum essentials necessary for existence. The mere presence of someone else in the room could trigger PEM, and it may lead to life-threatening situations.

Note: Any person who has PEM could end up very severely affected!

The inhumanity that is trying to avoid PEM

Avoiding PEM is crucial because, as mentioned, many instances of it might worsen one’s baseline and decrease chances of improvement or recovery.

However, avoiding it becomes extremely difficult and inhumane as the severity increases. Imagine being forced to choose between brushing your teeth or messaging a friend, knowing either could send you into weeks of increased unfathomable levels of misery and suffering.

Lying in a dark, silent room 24-7, restricted to 20 minutes of screen time a day, is torture, and these are the choices people are forced to make.

PEM in everyday life

In milder cases, it can still be difficult to avoid depending on an individual’s circumstances—a single mother with mild ME/CFS who has young children and little support might still find it very difficult to avoid PEM. Therefore, her risk of a decline increases.

On the more extreme side, there have been reports of people experiencing PEM from the automatic process of digestion! This severity can lead to conditions like gastroparesis, and people become at risk of starvation—PEM has killed people.

Why a widespread understanding of PEM is so important

PEM is real. It’s debilitating. Understanding it is the first step to building a world where those affected thanks to ME/CFS or Long Covid can get the care and compassion they deserve.

We urgently need research to pave the way for medical treatments. Trying to live with energy limitations is a cruel fate that isn’t necessary for anyone.