Acrophobia is the phobia, or extreme fear, of heights. It can include the fear of flying in an airplane, being on a bridge, or even going upstairs. There are different variations of the phobia. There is a designated fear of flying, which is called aerophobia. Acrophobia is the fear of not being on the ground and whatever falls into that category. It can be extreme or mild or anything in between. It stems from the way the brain processes information and how dramatic the fear becomes when signals are sent within the brain.
No two people process the same. The brain can send a signal of flight or fight, old brain behavior, because it senses things are not alright, such as with heights. This causes high anxiety and can even produce physical symptoms within the body, like throwing up or a rapid heartbeat. Such disorders are both mental and physical. Phobias can be treated, though. Therapy and other techniques may help.