Śivasaṃhitā 3.60

Paricayāvasthā has an exquisite technical definition in this verse: the vāyu (air, prāṇa) that normally alternates between iḍā and piṅgalā — moon and sun, left and right nostrils — stabilizes in suṣumnā, the central channel running along the spinal axis. No more alternation: prāṇa has found its natural course, the true channel that iḍā and piṅgalā’s duality always concealed.

Paricaya (intimate knowledge, profound familiarity) is the term naming this stage. Not conceptual knowledge but lived familiarity, that which emerges from such prolonged coexistence with something that its nature becomes transparent. The yogin in paricayāvasthā knows prāṇa like an intimate friend who no longer needs to be controlled: one simply lives with it.

The «ether of the suṣumnā tube» (suṣumnānāḍīākāśa) is one of the most specific concepts in tantric yoga. Ākāśa (ether, space) within the suṣumnā channel is not ordinary ether but cidākāśa, the space of pure consciousness. When prāṇa moves through that space, it encounters no resistance from the nodes (granthis) that obstruct circulation in the lateral channels. Movement becomes free, frictionless, natural.