I feel your pain mate.
about breathing in my case it was hyperventilation so you must force urself to breath in as much as you can, then hold your breath as much as you can (for example I can do it 30 seconds, regular is maybe 10 seconds keep doing it, in time you will improve ur time very fast) and breathe out. You will see immediate improvements in less and less need to take a deep breath to feel the whole cycle of breathing . I already write in my previous post try on youtube austin goh it is very nice explained and easy to do it.
Also you can try to mediate. Think something nice when you breath in and think on something unpleasant when you breath out. For example beautiful sunbeams and grey smoke.
Dont forget to check do you breath normal. Lay down put one hand on stomach and one on chest. Breath in and check, if you are stomach is raising you are good, if chests you must teach urself to do it by ur stomach.