Columnist and best-selling non-fiction author Michael McGirr writes in Tales from the Land of Nod:

In the history of human civilisation, sleep is the unrivalled hero. It is the wellspring of creativity. In sleep, we are most ourselves because we have to surrender our egos. It is the space in which so much happens, mainly because, while we are asleep, we cannot squeeze any extra appointments or make any extra phone calls or look at one more thing on the internet. Sleep is the daily visit that people who live in crowded dairies make to a wide open space.