You might try this 3 part breathing exercise when you feel you are having breathing problems due to anxiety.
Find a place where it's quiet. Sit in a straight back chair with both feet on the floor or lie on the floor with a straight spine. Begin inhaling by expanding the abdomen (let it inflate like a balloon), then move the breath into your rib cage and, finally, all the way into your upper chest. Exhale by reversing this action; begin at your collarbones and exhale down through your rib cage and into your abdomen. Contract your abdominal muscles as you finish exhaling. You might find it helpful to lightly place your right hand on your abdomen and your left hand on your rib cage to help direct the breath on its journey. Begin by practicing for one minute and then gradually lengthen the practice to five minutes.
This technique helps to eliminate shallow chest breathing and encourages full exhalation and inhalation.
Once again, there's no need to push yourself or judge yourself for being anxious. The idea is simply to be quiet for a short time and notice your breath.