beauty sleep
n//ˈbjuti ˌslip//skönhetssömn
(uncountable) Originally, sleep taken before midnight, on the belief that early sleep hours conduce to beauty and health; now (chiefly, humorous) , sleep at any time needed by one to stay beautiful; (countable) an instance of such sleep. [from early 19th c.]
(uncountable, chiefly, humorous) Extra sleep; also (generally) , any sleep; (countable) an instance of this; an extra nap.