Deep Sleep Meaning

Example : Used other than as an idiom: see deep,‎ sleep.2004, Robert Doherty, Area 51: Legend[1], ISBN 0440237254:  Donnchadh and Gwalcmai, along with the other fourteen teams selected for planetary infiltration, had been put into deep sleep shortly after liftoff from their planet.2005, Bob Ticer, Visiting the Strange Planet Called Earth, ISBN 1589397347, page 13:  The Kironian had remained in deep sleep until alerted by a high-pitched squeaky sound. When the Kironian woke, everything seemed as though it had just left Kiron.2008, Cavin Wright, The Golden Prize, ISBN 160693046X, page 17:  There is also the possibility that our aliens perfected cryogenics and simply went into deep sleep until the environment improved.