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Acquisition of various siddhis (psychic powers) may also result, but the practitioner is warned against their influence, and recommended to chant Pranava (the mantra Om) to get rid of the associated negative samskaras. This is only the first stage (arambha avastha) of kevala kumbhaka, and if the practice of nadi shodhana is continued, the second stage (ghata avastha) takes place (YSD v. 178-180):
प्राणापानौ मनोवायू जीवात्मपरमात्मनौ । अन्योन्यस्याविरोधेन एकतां घटतो यदा । तदा घटाद्वयावस्था प्रसिद्धा योगिनां स्मृता ॥
When the unity of prana and apana, manas and prana, and atman and paramatman is attained and their distinctness removed, this stage is called ghatadvayavastha or ghatavastha, for which a regular practice of restraining and sustaining prana is essential. This stage is known by yogis only.
At this stage, the yogi may practice the pranayama only once a day. This leads to pratyahara, described by Dattatreya as a practice where sensory withdrawal has been perfected to the extent that the yogi feels that whatever he sees, hears, smells, tastes or touches is the Supreme. The Shiva Samhita describes it as a stage where the yogi can hold the breath for three hours (3:57). The next stage of parichayavastha comes only when the yogi has mastered this stage (YSD v. 212-215):
ततः परिचयावस्था जायतेऽभ्यासयोगतः । वायुः सम्प्रेरितो यत्नादग्निना सह कुण्डलीम् ॥ बोधयित्वा सुषुम्नायां प्रविशेदविरोधत: । वायुना सह चित्तं तु प्रविशेच्च महापथम् ॥
The stage of parichayavastha comes thereafter if the yogi continues the yoga practice. The prana, acquainted with internal fire, awakens the kundalini and enters without obstacle into the sushumna nadi; the mind also enters into the great path with the prana.
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