There is another group of sufferers who experience panic attacks apparently spontaneously. This can often be associated with general anxiety - the ongoing grumbling of symptoms coming to a peak. But panic attacks are also known to just occur out of the blue. When this happens the fear of it re-occurring in the same situation can easily develop, and so a phobia or general anxiety can be the result. As is so often the case, the anxiety becomes self-feeding.
Some phobias are more common than others.
These are referred to as the simple phobias. Social phobia is less common, about 25 people in a 1000 will experience it per year. Agoraphobia occurs in about 30 people in every 1000 per year - it is roughly twice as frequent among women. The occurrence of panic disorder is between 10 and 30 people per 1000 in a year - again, it's roughly twice as frequent among women. The first step to dealing with phobia and panic is to break the vicious cycle that builds up.