The relaxed state vs. stress mode
Practice breathing deeply from your abdominals. Can you feel your belly button pull away from your spine as you breathe in? Can you feel your back expand just a little? (Imagine you are wearing a pair of high-waisted pants... feel the waist band get tighter in both your stomach and back.)
Practice breathing like this for just a minute every day. The more you practice it during times of calm, the more you will be able to pull it out as a tool during times of anxiety, stress, triggering, etc.
Bonus for childbirth prep
If you are pregnant, try practicing this calming abdominal breath. As you get closer to birth, imagine your belly expanding and creating space for the baby to travel lower.
You can use this breath during contractions, or surges, to relieve the tightness. Breathe out your belly and visualize the ribbons of muscles expanding to allow labor to progress and the baby to just fall right out.