It's important to remember that these attacks are triggered from something. For me, when I had panic attacks, it would be from knowing I was about to converse with a specific teacher at school, which for an unbeknownst reason, triggered anxiety and panic attacks. It is completely irrational. In the animal kingdom anxiety equals to 'fear' but usually we are not afraid of our triggers, we are afraid of panicking uncontrollably for no reason, and with no control. It helps to remember in the midst of, or just before panicking that the feelings are not real. You are not dying, there is nothing wrong with you, and you need to help yourself relax in any way possible and that works for you. But over and above everything, remember the irrational fears that plague you are simply that. Irrational, untrue and unharmful. Ask yourself what could possibly cause you to suffer a heart attack at the prime age of 25. A quite rare occurrence. You are panicking at the mere thought, and thoughts are just that. Thoughts. You can think anything you want, it does not make them real. Sometimes panic attacks become a pattern where you are waiting for the next step to happen. From the increased heart rate to the faint-headed feeling, to the paranoia and shock. Try nip it in the butt from the first sign, without letting your thoughts go to "It's happening again" or anything that might increase anxiety. This can be done by distracting yourself, look around, what can you see that distracts you or eases some anxiety. What can you smell, see, hear or feel? A small distraction might stop the path of panic, but always always always remember that you are in control of yourself however uncontrollable you feel, you are the only one in charge of your body.
Best of luck x