Fatigue Syndrome, ChronicDown SyndromeFatigueSyndromeXenotropic murine leukemia virus-related virusMental FatigueKansasFibromyalgiaRetroviridae InfectionsPersian Gulf SyndromeDNA ContaminationMuscle FatigueGammaretrovirusCognitive TherapyNeurocirculatory AstheniaMultiple Chemical SensitivityCase-Control StudiesSick RolePostural Orthostatic Tachycardia SyndromeSeverity of Illness IndexDyssomniasCentral Nervous System SensitizationSomatoform DisordersHerpesvirus 7, HumanEnvironmental IllnessChromosomes, Human, Pair 21QuestionnairesMetabolic Syndrome XInfectious MononucleosisTreatment OutcomeExercise TherapyPrevalenceMetanephrineAcupuncture PointsPainDepressionLeukemia Virus, MurineDiseases in TwinsExercise