Generally, a panic attack happens as a result of extremely heightened anxiety. Any of us have the potential of experiencing a panic attack. However, for those who do not suffer from any anxiety disorder, a panic attack is only likely to happen if triggered by an anxiety-provoking event. A panic attack can come on very suddenly and have no obvious triggers. Although a panic attack episode may appear at random, they come from our evolutionary response to danger. Having a panic attack is said to be one of the most intensely frightening, upsetting and uncomfortable experiences in a person's life. The American Psychological Association says the symptoms of a panic attack generally last for about 30 minutes, although the attack itself may only be 15 seconds long. Some panic attack can last for much longer, even hours. Panic attacks are associated with agoraphobia - fear of open spaces, as well as the fear of being unable to escape from a dangerous situation. People who have experienced a panic attack often say afterwards that they felt trapped.What causes panic attacks?

Experts say that anxiety and panic, to a certain extent, are a necessary part of our survival. However, when levels become so high that they undermine our thought processes, we naturally become afraid of them. When our brains receive a massive surge of nervous signals designed to warn us of imminent danger, the Amygdala, a part of the brain, is activated. The Amygdala controls our anxious response. Some people's Amygdala reacts with anxiety when there is no imminent danger, making it much more likely that they will experience high anxiety and panic attacks. When we are given the signal to react with anxiety we produce Adrenaline (epinephrine). Adrenaline is released in the Adrenal Glands. Some people call adrenaline the "fright or flight" hormone. A release of adrenaline into your system can raise your heartbeat, make you sweat, churn your stomach and provoke irregular breathing - all characteristics of a panic attack. If there is no imminent danger and your system is loaded with Adrenaline, that hormone will not be used up for running away - the build up can cause a panic attack.

Source: http://www.medicalnewstoday.com/articles/8872.php