The contents of these statements rest on ignorance on the prognosis. One group of patients who gets better over time. Another group who stays the same over time and 3. One group who gets worse over time. However, it is not easy to give relative sizes for the three groups, as even the methods for this dividing into groups is subject to uncertainty.
Some patients have changing symptoms from time to time and over the years.
Maybe in one period of time the IBS symptoms resolve somewhat, while the cognitive symptoms and the sleep problems increase in severity. During a different period of time, it is the other way around. One 2000-study demonstrated worsening of cognitive symptoms over time here. Another demonstrated CFS-symptoms to be continuously present for years here. There is no evidence that CFS, at least in the very short term, has a lethal course.