Panic Disorder is an anxiety disorder which is characterised by the presence of recurrent, unexpected panic attacks which is followed by at least 1 month of persistent concern about having another panic attack, or significant behavioural change related to the attack. For example people who experience panic attacks often change their behaviour by not going to the places in which they have had previous attacks in the hopes that they may avoid further attacks (i.e. avoiding public transport, lifts, movie theatres, shopping centres etc).
People who have panic attacks often are not aware that they are experiencing an anxiety attack and can misinterpret the signs of anxiety as signs that they are suffering from a serious medical condition (e.g. misinterpreting their increased heart rate and muscle tension in the chest as a sign that they are having a heart attack, thinking that the hyperventilation they are experiencing is the result of an asthma attack and that they may suffocate/stop breathing, or thinking that the blurred vision they are having is a sign that they may pass out). Consequently, many people who have panic attacks fear that they may die during one of their attacks and may only present for treatment after several trips to the doctors.
Some people with panic attacks may also experience agoraphobia. Agoraphobia is anxiety about being in places or situations from which escape might be difficult or embarrassing (such as a movie theatre, public transport, or staff meetings) or in which help may not be available in the event of having a panic attack (i.e. going out in public alone).