Deep sleep is the mental fluctuation that has absence of content as its support.

Nidrā (deep sleep) is recognized as a specific mental state, not simply the absence of mind. Patañjali considers it a vṛtti because upon waking we know that we slept — there is a witness that registers that experience of emptiness.

Abhāva-pratyaya-ālambanā means that the cognitive support of this state is non-existence or absence of other mental contents. Deep sleep is characterized by tamas (inertia), unlike samādhi which is luminous and conscious.

This distinction is crucial: although in deep sleep fluctuations temporarily cease, it is not liberation because ignorance persists in latent form.