Hmmmm...that's a new one on me, and I'm well acquainted with acrophobia, since I've been married to a sufferer for 33 years who claims he's nervous just being as tall as he is.
(As an aside, it was a verification of the true love he claimed he felt for me when I dragged him on the mule-back trip in the Grand Canyon, which included the beasts walking on a two-foot-wide path called Skeleton Point that had 4000-foot drop-offs on both sides.)
I was curious since DH has no trouble on ladders or ropes like you do, and Wikipedia had this:
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. Moderator cut: too long a quote, 1-2 sentences and link
It might be worth your while to discuss this with your doctor and undergo some balance-testing, along with asking if you qualify for any clinical trials that are researching this phobia. Good luck!