It is not clear what causes panic disorder. In many people who have the biological vulnerability to panic attacks, they may develop in association with major life changes (such as getting married, having a child, starting a first job, etc.) and major lifestyle stressors. There is also some evidence that suggests that the tendency to develop panic disorder may run in families. People who suffer from panic disorder are also more likely than others to suffer from depression, attempt suicide, or to abuse alcohol or drugs.

If you have anxiety that’s severe enough to interfere with your ability to function, medication may help relieve some anxiety symptoms. However, anxiety medications can be habit forming and cause unwanted or even dangerous side effects, so be sure to research your options carefully. Many people use anti-anxiety medication when therapy, exercise, or self-help strategies would work just as well or better—minus the side effects and safety concerns. It’s important to weigh the benefits and risks of anxiety medication so you can make an informed decision.
Although breathing into a paper bag was a common recommendation for short-term treatment of symptoms of an acute panic attack,[45] it has been criticized as inferior to measured breathing, potentially worsening the panic attack and possibly reducing needed blood oxygen.[46][47] While the paper bag technique increases needed carbon dioxide and so reduces symptoms, it may excessively lower oxygen levels in the blood stream.
Panic attacks can occur unexpectedly during a calm state or in an anxious state. Although panic attacks are a defining characteristic of panic disorder, it is not uncommon for individuals to experience panic attacks in the context of other psychological disorders. For example, someone with social anxiety disorder might have a panic attack before giving a talk at a conference and someone with obsessive-compulsive disorder might have a panic attack when prevented from engaging in a ritual or compulsion.  
The degree of accompanying stress response and its physiological, psychological, and emotional changes are directly proportional to the degree of anxiety. For example, if you are only slightly concerned, such as being slightly nervous about meeting someone new, the body produces a small degree stress response. The small degree stress response can be so slight that you don’t even notice it.
Some people find that medication alone can be helpful in the treatment of Generalized Anxiety Disorder, while others are more likely to benefit from psychotherapy. Some find that the combination of psychotherapy and medication is the best course of action. Engaging in certain behaviors may also ease your anxiety and promote a healthier lifestyle. These include:
People with panic disorder often worry about when the next attack will happen and actively try to prevent future attacks by avoiding places, situations, or behaviors they associate with panic attacks. Worry about panic attacks, and the effort spent trying to avoid attacks, cause significant problems in various areas of the person’s life, including the development of agoraphobia (see below).