I would not characterize myself as acrophobic, but every once in a while, I get a twinge of panic from heights.  My step-dad was a roofer.  Sometimes I couldn’t go near the edge.  Sometimes I would jump off.  Just no telling.  But the one time they asked us to shimmy out on the rafter above the lab, I freaked out.  Ultimately, I gave up on the task of cleaning and just got to the other end asap.  My friend was having the time of his life, brachiating from girder to girder.