Post-Exertion Malaise

A disproportionate worsening of symptoms following physical, cognitive, or emotional exertion that would not cause comparable effects in a healthy person. Post-exertion malaise is a hallmark symptom of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and occurs in many other chronic illnesses. The onset may be delayed by hours or days, making it difficult to predict. PEM is a key example of action-determined variability in chronic illness and illustrates why consequence-based accessibility — designing for the aftereffects of an action, not just the ability to perform it — is essential.