Deep sleep is that state of mind which is based on an absence [of any content]
Abhava-pratyayalambana vrttir nidra (in Sanskrit)
The Yoga Sutras - Chapter 1, Sutra #10
Let us continue our study of the Yoga Sutras.
Five types of “vrttis” or changing states of mind such as right knowledge, error, imagination, sleep, and memory, constantly absorb the pure consciousness or our soul away from its pure nature. Today we will focus on the fourth vrtti - sleep (“nidra”).
The fourth vrtti being discussed in Yoga Sutras does not refer to the state of mind represented in the dream state of sleep. Dream state corresponds to the fifth vrtti, memory, as it involves the activation of samskaras, or mental impressions.
In Yoga Sutras, nidra, sleep, refers to deep dreamless sleep only. The deep sleep happens only when the tamastic element of the mind densely covers the sattvic nature of the intellect (buddhi).
During the deep sleep the pure consciousness (or our true self) is never “switched off”, it is always fully aware, but, in the dreamless state of a sleep, its object of awareness is tamas (hence, there is nothing to recollect when one awakens, there is no dream recollection because of the inert essence of tamas).
If the tamastic element that covers the intellect during deep sleep is accompanied by a measure of sattva, a person feels refreshed and lucid upon awakening; if accompanied by rajas, one feels that one has slept restlessly; if tamas has almost completely dominated sattva and rajas during sleep, one feels tired upon awakening.
Next time, we will discuss the fifth changing state of mind, which is memory.