Everyone starts off with a fear of heights, right about the time when you are beginning to crawl as a baby. This fear of heights is instinctive and protective, especially at a time when a baby is crawling and is mobile. After infancy, what differentiates those who have an extreme fear of heights from those who have a normal fear of heights is that those with an extreme fear of heights have illogical thoughts and avoidant behaviors that feeds the extreme fear of heights.
Fortunately, for those with an extreme fear of heights (also known as acrophobia), there are effective treatment options that will help with your fear, such as CBT (cognitive behavioral therapy).