My experiences, which I’ve discussed at length on The Other Forum, have led me to read up a bit about Periodic Paralysis. Reading more I feel like it might well have some biological connection to ME and/or POTS. The name is slightly misleading, it does involve symptoms other than paralysis which can include brainfog, phases of weakness and delayed reaction to exercise. They seem to have something like PEM though there are variations in how it expresses. If you read this account, she could easily have been misdiagnosed with ME: http://fightinghkpp.blogspot.co.uk/2012/05/the-battle-against-periodic-paralysis.html I’ve definitely had very similar experiences, as well as more full on paralysis. Although my stamina is very limited, what most intrigues medics is my changing strength. I can have an abnormal neuro exam and EMG showing proximal weakness, then another day I can have a normal neuro exam. I can walk up and down stairs like a healthy, then an hour later not be able to walk a step. .