Just saw a retrospective/interview of Robin Soderling on Tennis Channel. It mentioned mono and repeated attempts at a comeback but never fully recovering. No diagnosis other than mono was mentioned, which seemed odd. "He retired early from professional tennis in 2015 due to health concerns." If he has ME/CFS, it must be mild, as he apparently only seems to have issues during intense training (says he's 80 or 90%). I see it's on Youtube.