Yoga Nidra is a yoga practice and it is the result of that practice such that the journey is the destination.
Patanjali’s Yoga Sutra 1.2 states ‘Yoga is the cessation of the modifications of the mind’. This sutra denotes both the process of dissolving mental modifications (i.e. modes of perception, sensations, psycho-emotional states, etc.) into the ‘mind-field’ (citta) and the result as mental treanquility wherein Awareness is pure and unmodified.
In this light it is clear that the practice of Yoga Nidra is Yoga as the union that is Presence when the ‘doer’ is relaxed-absent. In other words the mind is silent yet nothing has been lost; instead there is a clarity as seeing without the distortions or modifications that come from seeing through the lens of knowledge, memory and experience.
Thus Yoga Nidra is the practice of ‘yogic sleep’ as a means of being awake as your true nature.