That's the sound of stress leaving your body, of your brain functioning more optimally, and of better sleep at night.
And it can happen in as little as 30 seconds.
Yep. That works out to 4 breath cycles.
The more you do it, the more it works, and the more relaxed you will feel as a result. If you feel light-headed as a result, stick with it. It will go away as you continue to practice.
Dr. Weil suggests doing it a minimum of 2x per day, and a maximum of 4 breath cycles at a time. Once you become familiar with the technique, you can work up to 4x per day and a maximum of 8 breath cycles.
Use it when you're feeling overwhelmed or anxious. When you're having a craving (for a cigarette or sweet something-or-other). Or when you're needing to feel more grounded. It can also help to improve circulation and digestion.
So, sit back. Relax. And get your deep breathing on.