Anxiety is a behavioral response to stress. Although it is useful in some circumstances as it helps us prepare and react to certain problems or urgent situations that may arise, it can become so intensified to the point that it becomes a disorder. 

Anxiety disorder differs from general anxiety in that those who suffer from the condition tend to feel overly anxious or afraid to the point that it negatively affects the way they lead their lives, often causing the sufferer the inability to lead a normal life.