Anxiety is adaptive if it motivates effective behaviours, but if the behavioural component becomes maladaptive, it is referred to as an anxiety disorder. Generalised anxiety disorders occur in the absence of any precipitating stimulus. Phobia anxiety disorders are triggered by exposure to particular objects or situations. Panic disorders are rapid-onset attacks of extreme fear and severe stress symptoms (e. g. choking, heart palpitations). Obsessive-compulsive disorders are characterised by frequently recurring, uncontrollable anxiety producing thoughts (obsessions) and impulses (compulsions). Posttraumatic stress disorder is an ongoing emotional reaction to an extreme psychological trauma. People with panic disorder suffer from episodes of acute and unremitting terror characterised by recurring panic attacks. Physical symptoms of panic attacks include shortness of breath, perspiration, irregularities in heartbeat, dizziness and faintness. The victim of a panic attack thinks he/she is going to die. Between panic attacks, the person will experience anticipatory anxiety: the fear that another panic attack will strike.