When practicing Chi Kung breathing, remember to touch the roof of your mouth with your tongue while touching the lips together very lightly. Breathe in the nose and out the nose, in general.
There are some breaths that require you to exhale through the mouth, though. In that case, breathe in the nose (tongue to the roof of your mouth) and then, simultaneously, open the mouth, drop the tongue down and exhale gently.
In either case, your breathing should be gentle and patient — and comfortable. Remember, do not breathe to the maximum whether it is inhaling or exhaling. Again, remain comfortable; keep your breathing very rhythmical, smooth, relaxed and light (not heavy).
Chi Kung practice should make you feel better, not worse. If you are experiencing light-headedness, nausea, fatigue or any other unusual (negative) feeling, you are most likely doing something incorrectly. Generally that would fall into the category of tensing or straining yourself by over-trying. Just relax: let go of your entire body. Go with the breath. Follow its lead.
There is nothing to try for. There is only breathing. Keep it simple: keep it comfortable.
