Centuries ago, Yajnavalkya used the analogy of “the great fish which travels along both banks, the nearer and the farther” while referring to the human consciousness which oscillates between the waking and the deep sleep state (Brihadaranyaka Upanishad 4.3.17). He wrote that when the Atman “rests in the intermediate state (of dream)”, it sees both states – waking and deep sleep (Brihad. Up. 4.3.9). In the state of dreamless sleep, the Advaita Vedantins saw evidence of the existence of Brahman; they reasoned that if a person feels refreshed after sleep, it must be because the Atman had temporarily united with Brahman .