Ana Sandoiu, ‘Insomnia: Why your brain may sleep without even knowing it’, https://www.medicalnewstoday.com/articles/321388.php, MedicalNewsToday, Healthline Media UK Ltd (3 April 2018)
The experience of sleeping without even knowing it is not uncommon among those with the condition. Scientists have identified the phenomenon and, although they did not fully understand it, labeled it ‘sleep misperception’. (…) New research (…) delves deeper into the mystery of sleep misperception and may have found an explanation for it. (…) The reason behind why scientists have been missing out on the explanation for this phenomenon is that, traditionally, sleep is understood as a categorical experience: you’re either asleep or you’re not, and when you’re asleep, you cannot be conscious. (…) The question is: what role does conscious awareness have in our definition of sleep? (…) The study found that people with insomnia who reported that they had been awake, even when the polysomnography showed otherwise, had increased activity in brain areas associated with conscious awareness during the dreamless phase of sleep — that is, non-rapid eye movement sleep.