It is quite common to suffer from more than one anxiety disorder at once. This is known as co-morbidity. In a recent Anxiety UK membership survey, 70% of respondents identified themselves as suffering with the symptoms of 3 or more anxiety conditions. Labels for disorders can be helpful when trying to seek out information, but most people can have elements of many different conditions.
Many agoraphobics, for example, find that their problems started with panic attacks and panic disorder, and obsessive-compulsive disorder sufferers may also have generalised anxiety disorder.
What links all the disorders is an increased level of anxiety which the brain channels into an irrational fear or pattern of thought.