What does pathological fear mean?

Fear is a basic emotion that causes a person to either run away or become aggressive to defend against an attack. Pathological fear is a fear so severe and debilitating that it significantly interferes normal daily life functions. For instance, some people have a pathological fear of open spaces (commonly called agoraphobia) that can be so severe that they cannot leave their houses to check the mail box - the open space in the lawn is too much for them to handle.