Narcoleptic patients were compared to idiopathic hypersomniac patients and REM hypersomnia patients with regard to nocturnal sleep disruption. Results showed specificity of the narcoleptic sleep pattern and a possible correlation between REM fragmentation and cataplexy. Patients with and without periodic movements in sleep (PMS) were compared and no difference was found in their nocturnal sleep pattern, suggesting that PMS is not the major determinant of sleep disruption previously described in narcoleptic patients. Finally, nocturnal sleep disruption was treated with -γ-hydroxybutyrate (GHB) and results further indicate a possible link between REM fragmentation and cataplexy.