idiopathic hypersomnolencehypersomnolence disorder treatmentpathological hypersomnolencedaytime hypersomnolencedefine hypersomnolenceprimary hypersomnolenceidiopathic hypersomnolence syndromepersistent daytime hypersomnolencehypersomnolence meaningcns hypersomnolenceidiopathic cns hypersomnolencedown's syndrome information