Hi Miss Strange,
What usually happens right before you experience a panic attack? Does it usually occur at your workplace, home, right before an important dateline, in bed worrying about work matters etc etc? If you are aware of what comes into your mind right before it happens, jot it down. This could help you pin point out the stressor. You could consider recording down the specific details each time it occurs as you might find a common pattern after awhile.
Have you tried grounding technique? Whenever u experience those symptoms, try to identify 5 things you can sense around you - maybe 2 or 3 things you can see, 1 thing you can hear, 1 thing you can touch. Do these a few times alongside the deep breathing technique you have been using.
Ensure that you are eating well and getting reasonable amount of sleep every day. And try your best to include down time in your daily schedule - whether it's doing yoga, reading a book, listening to music or whatever activity you find relaxing/enjoyable.
Definitely suggests you consult a GP to rule out any medical condition. If this problem continues to persist and it starts to interfere with your ability to work/carry out daily task and you notice signs of social withdrawal/avoidance of specific places, don't hesitate to seek support from a professional. Your mental health is just as important as your physical health