Acrophobia (from Greek ἄκρος, meaning "summit") is an extreme or irrational fear of heights. It belongs to a category of specific phobias, called space and motion discomfort that share both similar etiology and options for treatment.
Acrophobia can be dangerous, as sufferers can experience a panic attack in a high place and become too agitated to get themselves down safely.
"Vertigo" is often used, incorrectly, to describe the fear of heights, but it is more accurately described as a spinning sensation, which may be caused by looking down from a high place, as well as by some other stimuli. Vertigo is qualified as height vertigo when referring to dizziness triggered by heights.
A possible contributing factor is dysfunction in maintaining balance. In this case the anxiety is both well founded and secondary. The human balance system integrates proprioceptive, vestibular and nearby visual cues to reckon position and motion. As height increases visual cues recede and balance becomes poorer even in normal people. However most people respond by shifting to more reliance on the proprioceptive and vestibular branches of the equilibrium system.
An acrophobic, on the other hand, continues to overrely on visual signals whether because of inadequate vestibular function or incorrect strategy. Locomotion at a high elevation requires more than normal visual processing. The visual cortex becomes overloaded resulting in confusion. Some proponents of the alternative view of acrophobia warn that it may be ill-advised to encourage acrophobics to expose themselves to height without first resolving the vestibular issues. Research is underway at several clinics.