No small art...

Living is a disease from which sleep gives us relief eight hours a day.
-- S. R. N. Chamfort

All men whilst they are awake are in one common world: but each of them, when he is asleep, is in a world of his own.
-- Plutarch

No small art is it to sleep: it is necessary for that purpose to keep awake all day.
-- Friedrich W. Nietzsche

Sleep that knits up the ravelled sleeve of care
The death of each day's life, sore labour's bath
Balm of hurt minds, great nature's second course,
Chief nourisher in life's feast.
-- William Shakespeare