Hypoventilation is breathing that is too shallow or too slow to meet the needs of the body. If a person hypoventilates, the body’s carbon dioxide level rises. This causes a buildup of acid and too little oxygen in the blood. A person with hypoventilation might feel sleepy. The kind of breathing generally practiced in most hatha yoga classes is called Ujjayi breathing, which loosely translates as “victory” breathing. This is not to say that the quality of the breath should be aggressive, but rather that there is a steadiness, resonance, and depth to it.