At the extreme spectrum of consciousness during sleep, some patients with rare hypersomnias reported experiencing a specific night ‘blackout’ when sleeping, i.e., an absence of experiences or recall of them from sleep onset to offset. Thus, we explored through questionnaires the conscious experiences (dreaming experience, mind, self) during the night in 133 patients with idiopathic hypersomnia, 108 patients with narcolepsy, and 128 healthy controls. The night blackout was more frequent in idiopathic hypersomnia than in narcolepsy and control groups. Patients with idiopathic hypersomnia and frequent night amnesia had lower dream recall frequencies, and felt more often sleep as deep and mind as blank during the night. They had a higher proportion of slow wave sleep on their (retrospectively collected) sleep recordings than those without night blackout. This night blackout provides a new model for studying loss of consciousness during sleep, here as a contentless, selfless and timeless feeling upon awakening.
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