Twenty-Five Doors to Meditation

 In normal activities, most people never realize they are breathing. If their breath and thought can combine, however, not only will individuals become clear about their breath, but they will also become extremely mindful of their other body sensations. Since mindfulness is a cultivation method in itself, the principle of keeping the mind in tune with the breath while remaining relaxed, detached, and aware is found in many cultivation schools and techniques. But in this technique you must not fall into sleepiness or torpor, and your thoughts mustn't remain scattered as in everyday activities. Normally we're always in either one of these two states—torpor or drowsiness, or the excitedness and restlessness of mental involvement. However, you try to abandon these two states when you're practicing observing the breath. At the beginning of genuine anapana breathing exercises, one just watches the breath. After a very short while, the breath will calm down to become long and soft. As this external breathing dies down to a point of near cessation, the chi of the inner body will start to become more activated. That's because the extreme of yin (stillness) will give birth to yang (movement), which in this case is chi. However, this internal chi is not the same as the external wind used in respiration. Rather, it's the real chi of the body which has tremendous power because it can transform the physical nature and is connected with consciousness. When the expiration finally ceases and the mind quiets down, we then arrive at shamatha. This is the state of stopping or halting found in cessation and contemplation practices.

Bodri, William; Shu-Mei, Lee. Twenty-Five Doors to Meditation: A Handbook for Entering Samadhi (p. 26). Red Wheel/Weiser. Kindle Edition.