Understand Chronic Fatigue Syndrome

5. PEM

PEM stands for post-exertional malaise, a generalized state of weakness that occurs after physical or mental exertion. By definition, the malaise and weakness last for at least 24 hours after a person exerts themselves. It is one of the classic symptoms associated with CFS, and one of the most debilitating. People who experience PEM typically describe it as a combination of fatigue and achiness. Some people also develop brain fog and flu-like symptoms. PEM normally develops after an intense period of physical or mental activity, such as going on a hike or taking an exam. Sometimes, the onset of PEM takes a few days, and it may persist for days or weeks at a time.