PEM stands for post-exertional malaise (pronounced ma-LEH-eez). It is defined as an increase in symptoms (for example, fatigue, brain fog, breathlessness, headaches, body aches) after what doesn’t seem like a lot of activity. 

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The activity can be:

• physical (like taking a walk)

• cognitive (like doing paperwork)

• social/emotional (like attending a dinner party)

 

It might seem like you feel a lot more fatigue and overall symptoms than you think you should, based on the level of effort or time you spend doing an activity.