Anxiety may be caused by a mental condition, a physical condition, the effects of drugs, or from a combination of these. The doctor's initial task is to see if your anxiety is caused by a medical condition.
Common causes of anxiety include these mental conditions:
Panic disorder: In addition to anxiety, common symptoms of panic disorders are palpitations (feeling your heart beat), dizziness, and shortness of breath. These same symptoms also can be caused by coffee (caffeine), amphetamines ("speed" is the street slang for amphetamines when they are not prescribed by a doctor), an overactive thyroid, abnormal heart rhythms, and other heart abnormalities (such as mitral valve prolapse)
Generalized anxiety disorder
These common external factors can cause anxiety:
Stress at work
Stress from school
Stress in a personal relationship such as marriage
Stress from an emotional trauma such as the death of a loved one
Lack of oxygen in circumstances as diverse as high altitude sickness, emphysema, or pulmonary embolism (a blood clot in the vessels of the lung)
The doctor has the often-difficult task of determining which symptoms come from which causes. For example, in a study of people with chest pain that could be heart disease but turned out not to be heart related, 43% were found to have a panic disorder -- a common form of anxiety.