People who have panic attacks often have no control over when their symptoms will strike. For people with panic disorder, these attacks come on suddenly, without any warning or cause. Those with specific phobias may only have panic attacks when exposed to their specific fear; however, these feared stimuli may not always be easy to avoid.
Given that attacks can occur at any place or time, some people may try to jump in and help the person through the panic attacks. However, well-meaning friends, family, and even strangers may try their best to help, only to say the wrong thing to the person having the attack.
Read here for some ideas on what not to say to someone during a panic attack, and tips for what to say or do instead.