Targeting Skeletal Muscle Dysfunction With L Carnitine for the Treatment of Patients With Chronic Obstructive Pulmonary Disease In Vivo Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome Fatigue is a common symptom for people with and without Down syndrome. It involves feelings of extreme tiredness and lack of energy. Lifestyle factors such as diet, exercise, sleep, hydration, and stress L Carnitine: Benefits, side effects, and dosage