I don't know a great deal about MS admittedly, but from what i've read, relapses usually involve an exacerbation of symptoms followed by either a slow recovery/remission or sometimes a permanent worsening. This is thought to be due to damage to the myelin sheath (caused by the immune system). I couldn't help but see some similarities with the symptom exacerbation experienced in ME/CFS here. Is it conceivable that a similar thing happens during major ME relapses and even PEM? (not necessarily myelin shealth damage but some other damage, which isn't reversible in some/many cases)? I'd say that I was gradual onset and ME crept into my life slowly, before a seriously bad 'relapse' at the gym which changed my baseline from about 85% to 30-40% functioning in a matter of hours. I always wonder what could have happened so rapidly in this timeframe that affected my physical/cognitive functioning so acutely. The fact that my executive functioning/information processing abilities etc haven't improved makes me wonder if the damage is permanent. Anyway, interested to hear your thoughts!