When we feel anxious, fearful, resistant, powerless, apathetic, angry, etc, our breathing is automatically altered. If we allow ourselves to get swept away in these emotional states and resist them, we close ourselves off from a rhythmic flow and the physiological response in our bodies is to match this closing off by also resisting the natural flow of our breath. Note: most negative emotions only last for 20-30 seconds if we simply accept them for what they are- just an emotion.
When you enter one of these states, feel the restriction in your lungs and focus on re-opening the natural flow of air. The key is to not resist the feeling but allow it to be there and then let it go. Breathe through the restriction you feel and allow the negative feeling to dissipate into the nothingness where it came from.