What is
PEM?
Post-Exertional Malaise
PEM is a delayed crash, occurring hours or even days after minimal exertion - physical, cognitive, or emotional - and is characterised by a worsening of multiple systems, not just fatigue.
The hallmark of PEM is that it is out of proportion to the activity that caused it and can take days or weeks to resolve. It reflects intrinsic biological dysfunction, rather than simple deconditioning.
Rest does not immediately reverse it, and “pushing through” often leads to a deeper, more prolonged crash.
Until there are better treatments, one way to describe PEM is that it is like sunburn. If you have bad sunburn you can’t fix it, but you can treat the pain and symptoms until it heals.