From the abdomen. If you're feeling your chest rise, you're breathing shallowly, which increases sensations of anxiety and puts you at risk of hyperventilating/feeling dizzy/breathless because you aren't expelling the maximum carbon dioxide.
Try this;
Get onto the floor (sequester cats, dogs and small children away somewhere else first before they attempt to supervise, assist or just leap onto you for fun).
Bend your knees so that your feet are resting on the sofa seat.
Allow your shoulders and upper back to rest against the floor.
Place your hands on your abdomen. If that makes you feel anxious, let them rest on the floor instead.
Try to gently blow air out between your lips towards your feet. Take your time, there's no rush.
If you can feel your breathing slow down, place your hands on your abdomen again and feel it move as you softly blow as though to make a candle flicker but not go out.
Keep going and if you feel calmer, try and pay attention to how it feels after you've blown and then allow yourself to take in some more air.
Do that until you're bored/feel better/you can hear the cat digging its way out of the bedroom and there are suspicious sounds of rustling where you relocated the dog into the kitchen with the full bill or unsecured bag of cat crunchies.
Don't scramble up, let yourself roll to your side and slowly press up with your hands. Take your time.