If you suddenly feel intense fear and anxiety and you have symptoms such as shortness of breath, sweating, nausea, trembling, numbness sensations, dizziness and overall feeling as if you're about to lose it and faint, you're probably experiencing a panic attack. If you know that you have a severe heart disease, call an ambulance immediately as some symptoms might be similar to those of a real heart attack. While a panic attack is basically harmless on a physical level, a heart attack can be fatal. Also, if you have asthma, an asthma attack could be the cause for your difficulties breathing so you should grab fast your quick-acting bronchodilator and use it.
When none of these two apply and you get a panic attack, you should first and foremost do your best to remain calm and don't get alarmed. If the fear has been provoked by a certain known reason, try to move away from that source of intense stress. For example, if you have a fear of heights or a trauma concerning heights and you find yourself on the rooftop terrace of a very high building, ask someone to help you get down.
Once you regain your normal breathing, the other panic attack symptoms will be easier to take down. Lack of carbon dioxide leads to hyperventilation, which aggravates anxiety. Usually the best thing to do is to grab a paper bag and breathe in and out. Doing this for at least ten times and then trying to breathe without the bag should do the trick. But let's be honest. Who carries a paper bag everywhere they go? So it's better to do a few simple breathing exercises such as rhythmic breathing (breathe in-breathe out) while trying to relax or counting numbers. Many people find it very comforting to lean their backs against a wall or to hold on to a very heavy object such as a table.
Anytime you feel you're having a panic attack, it's better to tell someone and allow him or her to help you. If there's no one around, fight it off by controlling it as well as you can. Remain calm, drink a bit of water and slowly breathe in and out until you feel it fades away.