Bearing in mind I do not have ME.
I was in the RAF when I caught Glandular Fever at the age of 18 in the early 1970s. I gather other cases could be a lot worse than mine, but nonetheless I was hospitalised for 2 weeks, given 3 weeks sick leave, and put on light duties for some time after that. Pretty sure I was told to take things easy. So I think there was at least recognition there was a risk of relapse, and that avoiding over exertion was the best way to avoid it.
Given that Glandular Fever is something a percentage of people are known to relapse with, and given it is often an original trigger for ME, I wonder if there is any commonality between GF relapsing and ME? Could they be two different facets of a common disease mechanism. Would it be something worth investigating?