As suggested by the above statements the origins and boundaries of the syndrome are still unclear. Illnesses that are consistent with CFS definitely occur in adults and adolescents. Whether or not the syndrome occurs as a readily recognizable illness in younger children is still an open question. Fatigue is a nebulous concept. It can be considered good or bad.
Good fatigue follows successful work or play and resolves within a finite period of time.
Bad fatigue may or may not have a predisposing event, and it may persist for unexpected periods of time. If it lasts for excessive periods, it might be considered as being chronic. If the chronic fatigue prevents the person from normal work or play, it becomes a liability and medical advice may be sought. Since fatigue is present in a wide variety of diseases, the health care giver tries to shorten the list by asking questions that may lead to a diagnosis or to the performance of confirmatory laboratory tests. More often than not, the answers to the questions or the description of the patient's other complaints are the key factors in establishing a diagnosis.