Acrophobia is diagnosed in several ways, but one is by a psychiatrist who evaluates you. To qualify, you must have the seven conditions. Marked fear or anxiety in regards to the situation or even the object is one requirement. The situation must always present a problem, not just part of the time. It must induce high anxiety or feat too and you must try to avoid the situation.
It is also a requirement that the condition has lasted over 6 months and causes impairment of some type. The condition must not be explainable by another mental illness or medical condition.