The Philosophy of the Upanishads c11.s3.t3.4

c11.s3.t3.4

Therefore it is said,—he should not be wakened suddenly, for it is difficult to find a cure for one to whom he fails to find his way back. Therefore it is said,—it (sleep) is for him only a waking state, for what he sees waking, the very same also he sees in sleep. Thus therefore this spirit serves for a light for itself.”