Anxiety is a universal human experience. For most of us most of the time the reasons for the anxiety are both obvious and understandable, and the anxiety will subside when the reasons depart or remain if they do not. For some people it is not as simple as this; they have anxiety disorders.
When is anxiety a disorder, rather than a normal event?
The level of anxiety is not a criterion for determining if it is a disorder. Those hotly pursued by lions will be anxious indeed, but their anxiety will be normal under the circumstances. Disability is not a criterion. If I have a phobia of giraffes I have an anxiety disorder, but if I stay away from the zoo I have no disability.
The need for treatment is no criterion. If I have survived a terrifying air disaster and my occupation makes it necessary for me to fly, then in all probability I shall need treatment before I can fly again. Nevertheless, the anxiety generated by the crash and attached to flying could scarcely be regarded as pathological. A normal state may require treatment.
The criterion is the appropriateness of the anxiety. If someone is terrified by the sight of a mouse, or a moth, then their anxiety is pathological, for it is extremely unlikely that either of these creatures will attack them and unthinkable that harm would arise if they did – and were it to come to combat, there would be no doubt about who would win.