Take in: 4-count. Be still: 7-count. Breathe it all out: 8-count. It will help to calm the nervous system with the responsibility of a natural tranquilizer.
Calm your body and pay attention to your breaths. Ensure the diaphragm is being engaged, and this will reduce the switch to the 'flight-or-fight' state.
Try to get a 4-second inhale, hold for 4, and exhale with 4. Also, imagine drawing a box in your mind. It helps you regain control and calm the mind.
Use gentle alternate nostril (nadi-shodhana) breathing. It can harmonize the body and mind, taking care of the stress and the anxiety you might be experiencing.
Mindfulness just loves your breath and its way to safety from panicattacksk. It requires every single sense of yours. Here in the present, panic is gone.