The Fourth Pranayama Transcends External And Internal Operations (1). 51.
(b) Pranayama has to be practiced by slow degrees, keeping an eye on health and physical well-being.
(c) Pranayama practiced without meditation makes the mind more restless. That is why, in some cases it brings on lunacy. If the mind cannot first be made vacant through meditation in respect of an internal region, it is preferable not to take to Pranayama. Pranayama may, however, be undertaken if the mind can be fixed on an image conceived in an internal region. For the practice of Yoga, however, the state of void is more suitable.
(d) Attention should be given to diet. Too much of food, physical exercise and mental labour diminishes chances of progress in Pranayama. Light food, keeping the stomach partially empty, is frugality in meals. Moderation of diet will be found discussed in books on Hatha yoga. Food containing carbohydrate should be taken, oil and fat should not be taken in excess.
The suspension of Prana, which either arrests modifications of the mind or makes it one-pointed, constitutes Yogic Pranayama. Periods of stability of the mind during the practice of individual Pranayamas, growing gradually and continuously, develop finally into Samadhi. That is why it is said that twelve Pranayamas make one Pratyahara, and twelve Pratyaharas make one Dharana etc. Therefore, unless the mind is steadied and made free from attachment to objects, it is not Yogic Pranayama. It would be only a physical feat. Mere suspension of breath is an external expression of Samadhi, not its internal or real characteristic.
By That The Veil Over Manifestation (Of Knowledge) Is Thinned. 52.
In the case of the Yogin engaged in practising Pranayama, the Karma which shuts out discriminative knowledge dwindles away (1). That (Karma) has been described in the following quotation: “The illusive magic of misapprehension covers the sentient Sattva (buddhi) by a thick veil and directs it to improper deeds.” The practice of Pranayama weakens and gradually attenuates that Karma of the Yogin which veils revelation and brings about the cycle of births. Thus it has been said: “There is no Tapas superior to Pranayama; it removes impurities and makes the light of knowledge shine.”
(1) The veil enveloping discriminative enlightenment which is worn away by Pranayama is not the veil of misapprehension but the veil of Karma based on misapprehension. Karma is the means of sustenance of wrong knowledge. Therefore attenuation of Karma attenuates misapprehension as well. Pranayama leads to immobility of the body and the organs. Its latency attenuates the latency of afflictive Karma just as the latency of anger is attenuated by that of non-anger. Thus is is clear that Pranayama weakens and causes the decay of the false knowledge based on Avidya (which is identification of the body or the senses with the self) and actions and latencies derived therefrom. Some people raise the objection that since wrong knowledge can be destroyed only by right knowledge, how can (physical) act in the form of Pranayama cause its destruction? In reply, it may be said that in this case also misapprehension is destroyed by knowledge. Pranayama is no doubt a physical act, but the knowledge gained by the act causes destruction of Avidya. The practice of Pranayama separates one’s I-sense from the body and the sense-organs. Therefore, knowledge corresponding to the act of Pranayama (every act has its corresponding knowledge) is ‘I am neither the body nor the senses.’
– “Yoga Philosophy of Patanjali” by Swami Hariharananda Aranya
Vastha Yogi 