One of our oldest traditions of physical culture and health holds an answer to one of our most modern of problems - anxiety. Although many us typically think of the physical practice associated with Yoga as a series of pretzel-like postures executed by impossibly flexible people, the core of the physical practice actually lies in breath control, or pranayama (pr., prahnah-YAH-mah). The combination of posture and breath is typically referred to as Hatha (ha - sun; tha -- moon) Yoga in the West.
Pranayama is a highly complex discipline that has many different aspects and includes a variety of very specific practices. One of the most common, and useful, pranayama practices is called nadi shodhana (pr., nah-dee SHOW-d'nah) or alternate nostril breathing. According to Ayervedic medicine, this practice is intended to purify the pranic channels of the body. From a less esoteric viewpoint, nadi shodhana brings the body -- and by association the mind -- into a state of balance and neutrality by activating the same energetic pathways that in acupuncture are associated with balancing the hemispheres of the brain. On an even less esoteric note, Western medicine has long known that, while mouth breathing tells the body it is in a state of stress, nostril breathing tells the body it is in a state of homeostasis. This strategy of nostril breathing=homeostasis has been employed by elite athletes for decades.
The practice of nadi shodhana itself is quite simple. The first rule: Right at night...when doing the practice in daylight, we start with the left nostril, after sunset, the right nostril. Secondly, the right hand is held in what is called Vishnu mudra; a hand position (mudra) in which the thumb and ring finger are active and the other three fingers remain relaxed.
While sitting comfortably, with the back straight, we close the right nostril with the thumb of the right hand (assuming it is daylight, else, reverse). We inhale gently, then, closing the left nostril with the right ring finger, we exhale completely on the right side and inhale again on the right side. We close right, exhale left, inhale left, close right, exhale left, and so on. The eyes should be closed, and attention paid to consistent posture.
The complexity within this practice comes from the iterations, or number of ‘rounds'. A ‘daylight round' would be -- in left, out right/in right, out left. A ‘nighttime round' would be - in right, out left/in left, out right. For practical purposes, one starts with 11 rounds, and increases by 11 every 7 days until reaching 121 rounds. This constitutes a complete practice that can be undertaken 3-4 times a day. The practice should be followed by 10 minutes of sitting concentration or sitting meditation, depending on the level of the practitioners' attainment. A single session, outside the regular schedule of practice, can be undertaken at any time as a 'panic fix'.
There are several more complex iteration schedules, which include kumbhaka (breath retention) that are applied to this practice, and a more detailed explanation is available in Path of Fire and Light, Vol. 1, pp. 32-36 by Swami Rama, available through the Himalayan Institute Press.
It is inadvisable to undertake a more involved pursuit of this practice than is described here without the personal guidance of a qualified teacher, or without a consistent asana and meditation practice in place.