HCRT and narcolepsy: Alternatively, it cannot be ruled out that N-1 is simply a heterogeneous condition, with some individuals exhibiting high sleep efficiencies and low arousal indices, but perhaps high REM fragmentation, etc. The heterogeneity observed in this study is one of the most valuable findings because most of the data published to date are on hypocretin-deficient (vs. not) narcolepsy cases, which may be an entirely different phenotype altogether than what is naturally observed in a sleep clinic setting.