Good reply txsha, I totally agree. The only thing I would add is that the breathwork is doing its job and bringing up in you what's just below the surface and needs to be healed and integrated. Anger comes from not getting something you wanted so while fully feeling the anger, ask yourself 'what was it I want or wanted and didn't get?'. This will lead you to the wanting behind the anger and to the deeper feeling and need which lies at its core, which is good and true.
Anger is not really a feeling, its an emotion or reaction, but fully experiencing the anger (with a pillow or something not a person) will lead you to the underlying feeling. When we are in feeling we will automatically breath fully again.
I previously had the username "ontheroad"