Nidrā

Sleep, the state of deep unconsciousness. In YS 1.38, nidrā is presented as one of the states of consciousness (vṛtti) that can serve as an object of meditation to stabilize the mind. In the Haṭha Pradīpikā, the yogin is cautioned against excessive sleep as an obstacle to practice. Nidrā is not mere unconsciousness but a subtle state with its own cognitive structure. See yoga-nidra.