In a 43-year-old man suffering from hypersomnia with sleep drunkenness, a polygraphic sleep study with direct measurement of blood pressure was carried out. The main findings were lack of blood pressure activation with arousals during the sleep period and persistence of sleep levels after morning awakening. This indicates that cardio-vascular responses to the needs of active behaviour are insufficient. Taking into account feedback mechanisms of blood pressure on alertness, this could be a cause for sleep drunkenness and daytime sleepiness. The blood pressure sustaining drug etilefrine seems to alleviate these symptoms.