Delta is another level down from Theta and in Delta, or deep sleep, your brain operates between 0 and 4Hz. The Delta state is associated with rejuvenation and healing, and is believed by many scientists to be the most beneficial brain state. Delta is deep, dreamless sleep below the level of REM (Rapid Eye Movement) sleep.which affords your brain and your body the opportunity to rest, repair and renew. It also facilitates a deeper connection to the subconscious mind and can permit very highly advanced awareness.  This state also stimulates the release of growth hormone.