Orthostatic intolerance (OI) is a common manifestation of autonomic dysfunction. It is characterized by light-headedness and palpitations in the upright position, with relief when supine. It can affect the quality of life. Other symptoms that may accompany OI include headache, fatigue, nausea, palpitations and abdominal pain. The prevalence and characteristics of autonomic symptoms in childhood hypersomnia disorders of childhood has not been examined, and hence were studied.