A panic attack usually occurs just when you are not expecting one.
Experiencing an attack is a really frightening ordeal and they can stay with you for some time.
I still remember just how overpowering my very first anxiety attack was.
When my heart started racing and the onslaught of sickness and dizziness kicked I didn't know what was happening, It was dreadful.
If you already get panic attacks then the following symptoms are nothing new to you but for anyone that doesn't I've compiled a list of the most common feelings that happen during a panic attack:

• Feelings of vertigo before panic sets in
• Tightness across the chest and throat- leading to a sudden shortness of breath
• Speeding up of your pulse rate with perhaps a slight stinging feeling around you
• A swell of anxiety with real feelings of fear and sickness.
  You may also feel incredibly warm or perhaps red blotches can appear
• Mood swings or increasingly negative/unwanted thoughts
• Feeling unconnected with your natural surroundings
• Feeling like there's nothing more you can do, the fear being so frightening that you might be tipped over the edge?

When you have a full on attack I suggest you try to stay as calm as humanly possible given the circumstances.
Maintaining a diary of several panic attacks over the course of a year also helped me realise the common situations that I had attacks.
Over the years after investigating nearly every book and medication on the market I came to the conclusion that there just isn't any real cure for panic attacks and anxiety, until recently.
If you have to live with panic attacks disturbing your life or maybe you have a relative or friend that does then I have some really great news!