According to Osho, there is no separate 'sleep chakra.' Each of the first six chakras has a sleep-and-wake phase (yin/yang), while the seventh, Sahasrar, is pure awareness and never sleeps; hence the yogi never sleeps though body and mind do. As energy rises through higher centers, sleep becomes deeper, quieter, and more relaxed.
There isn’t one sleep chakra; each lower chakra has a sleep/wake side, while the top chakra stays aware even when the body sleeps.