I had it too and sometimes when telling a stressful incident, situation or past trauma I still do. Awareness is the first step to initiating change. I had to teach myself to breathe "through" my stress/anxiety/fear/anger or other uncomfortable emotions.
"Chronic breath holding and effortful breathing are not healthy because the muscular effort, coupled with the effects of stress on the nervous, hormonal, and immune systems, can impair both physical and psychological function.
How can you help yourself overcome breath holding habits? One way is to take classes that have a component of breath awareness and control training, like yoga, tai chi, or meditation. These have the effect of activating the parasympathetic nervous system, replacing effortful with relaxed breathing, reducing pain, anxiety and depression, and enhancing re-engagement in everyday and occupational activities. Breathing meditation has been shown to have a positive impact on a variety of conditions including anxiety, depression, PTSD, mood disorders, addictions, and stress tolerance. Breath control has also been shown to reduce pain in childbirth and require less medical intervention.
But you don't need to specifically train your breathing to change your breathing patterns. Activating your body sense related to any internal sensation or emotion will lead to more relaxed breathing. Different emotions are associated with effortful vs. relaxed breathing, as well as with different variations of depth, duration, and rate of breathing.
Anger and fear are associated with effortful breathing patterns accompanied by tension in the abdomen and chest. Chronic and unresolved anger, aggression and hostility in childhood and adulthood is associated with breathing disorders such as asthma and shortness of breath, as well as cardiovascular disease.
Getting in touch with the body sense of pain and emotion in therapeutic and close interpersonal relationships can lead to more relaxed breathing, usually accompanied by sighing and feelings of relief and lightness. I actually think that breath control and breath meditation does not directly affect the breath, but works indirectly through the body sense neural networks (interoception and proprioception) that - when we slow down and pay attention to ourselves in the present moment -- stimulate whole body relaxation via reduction of stress hormones and activation of the parasympathetic nervous system. Paying attention to the breath is really no different from paying attention to anything in our bodies."