They have tested you for heart trouble, and you don't have it.
And chest pains and trouble breathing are well-known symptoms of anxiety, even if you have not had them before.
Perhaps nobody has explained to you that panic attack or anxiety attack symptoms are caused by hyperventilation. Hyperventilation means breathing too fast. Even a little bit too fast will do it. You may not think you are breathing very fast,, but it may still be too fast.
What happens is that you exhale too much carbon dioxide, thus upsetting the chemical balance of your blood. Unfortunately, this makes you feel as if you are suffocating, so you breathe even harder, and the symptoms just get worse.
In fact, hyperventilation will not harm you. You feel like you are dying, but nobody has ever died from this.
To feel better, you need to get more carbon dioxide into your bloodstream. Breathing more slowly would do this, but you can't do that, can you? You might do some vigorous exercise; that will produce more carbon dioxide for you. Or you might breathe into a bag, and re-breathe the same air in the bag until you feel better - in my experience, about 8 to 10 minutes, if you don't take any fresh air during that time. Maybe you can find another way to get more carbon dioxide into your system.