It enhances immunity as well as the cognitive abilities that may have aided our descent from apes
It was the Upanishads that introduced me to the kinds of sleep. The Mundaka and the Chandogya Upanishad talk of “four states of consciousness". The first was Awake, the second was Dream-Filled Sleep, the third was the much sought-after Deep Sleep, and there was a very mysterious fourth stage. Called Turiya, it is a stage which transcends sleep; in many texts, it was referred to as samadh (or samadhi), and is akin to the deepest form of meditation. Only achieved by the truly awakened, it was where the self or atman is realized.