The PWC may have times when symptoms are very mild. The outcome is the classic post-exertional relapse and often, an exacerbation of nearly all symptoms. The long-term prognosis of CFS is not well studied or documented. Prognosis appears to be as variable as symptoms. A small percentage of PWCs report total recovery with many others noting small to moderate improvements.
Some people never improve, while others actually see an increase in symptom severity.
The CDC states that if improvement occurs, it is generally observed within five years of illness onset. If there is no symptom improvement within these five years, it is statistically unlikely that the person will ever fully recover. It is likely that CFS is triggered by many different factors, and perhaps by two or more occurring together. Studies conducted on orthostatic intolerance, HPA axis disruption, and immune system activation appear encouraging. The symptoms of CFS are similar to other diseases with overlapping diagnoses, such as fibromyalgia, lupus erythematosus, multiple sclerosis, Gulf War illnesses, and multiple chemical sensitivities.