The word nyasa means ‘to place’. It is a practice in which specific mantras are ‘placed’ and felt at different parts of the body. It is the traditional form of yoga nidra used by yogis throughout the ages and still practised by almost all Hindus.
Nyasa is described in various scriptures such as the Brihad Yoga Yajnavalkya Smriti and the Yogataravali, as well as many upanishadic and tantric texts. The Aruneyi Upanishad (verse 5) advises all wandering sannyasins to practise nyasa at all times – to chant Aum and to place it mentally at different parts of the body. More specific and ritualistic forms of nyasa are described in the Mahanirvana Tantra. They include the following:
Matrika nyasa in which the letters of the Sanskrit alphabet (matrikas) are placed on different parts of the physical body of the sadhaka while chanting the corresponding sound.
Hridayadi sadanga nyasa literally means the placing of the hands on six different parts (sadanga) of the body beginning with the heart (hridaya). Specific mantras are chanted as follows: when touching the heart chant namah; when touching the head swaha\ at the crown lock chant vasat and so forth.
Kara nyasa in which mantras are placed and chanted on the fingers, thumbs and palms of the hands. (Note: most forms of yoga nidra that we teach include this type of nyasa, but without the mantras).
Vyapaka nyasa, all pervasive (vyapaka) nyasa. This form is so called because the energy of the mantras is distributed throughout all the parts of the body, together with awareness. Specific mantras are placed and felt on the head, mouth, heart, etc.