I know this isn't PEM, but it is kinda like a freakish distant cousin, and it is something I was not familiar with. A family member has been diagnosed with Andersen-Tawil Syndrome. Only about 100 individuals have been diagnosed with it world-wide. It is characterized by a triad of manifestations: Profound muscle weakness - to the point of paralysis, cardiac abnormalities - principally Long QT, and certain polymorphisms like scoliosis. The periodic paralysis/muscle weakness seems to be triggered by rest. So resting after exertion, or just prolonged rest, can cause an exacerbation of this particular part of the triad. It has something to do with potassium channels. I am still feeling my way around the specifics. But I had never heard of rest itself being a trigger mechanism to a worsening of some symptoms, and I wanted to run it by the community.