what little we know of it is mainly from hypnosis (named after Hypnos), from suffering, and from the study of dreams
Hillman uses the etymological derivation of ‘hypnosis’ from Hypnos to bind the Freudian id, as the depth dimension of psyche, to the mythological deity of sleep, thereby mythologizing the entire psychoanalytic concept of the unconscious.
, The Dream and the Underworld, 1979thesis