Claustrophobia can be defined as the fear of enclosed spaces or fear of being put into a small place where there is no escape route. This kind of condition is a form of anxiety disorder and can lead to a severe panic attack. Have you ever been put into a small place and you started developing extreme fear just become it was physically obvious there would not be a way out, that is Claustrophobia.
People suffering from this condition will always go to a great extent to avoid any circumstance that might lead them to being held up in a smaller place, they will never buy any suggestion to travel by subway all because they are afraid of any eventuality, they will rather prefer to go through stairs. The phobia is classified as an anxiety disorder because it leads to a state of mental uneasiness, apprehension in the person who has the phobia.