I think we need to take a cautious approach, though, since it's possible the broad phenomenon isn't even unique to people who go on to develop long-term symptoms. People making a slow recovery from glandular fever, who aren't familiar with PEM as a concept, may describe it the same way as ME patients do. Eventually, they return to their previous lives. There may be some aspects that are particularly associated with ME, but the overall pattern – the triggering of multiple symptoms that occurs after effort or stress, and following a delay – might just be one of the ways our bodies respond to certain circumstances. It would be useful to understand it better, of course, because it could give us important information about what goes wrong and why it doesn't right itself.