As distinct from heights in themselves. Chosen because I'm running a C-themed week in my journal. I get the impression this is not diagnosed very often, as it tends to get subsumed under acrophobia. Coined from Greek kremnos, overhanging cliff + phobos, fear.
My cremnophobia kept me from entering the slot canyon -- I couldn't stop obsessing over the possibility that those sheer walls would chose THAT MOMENT to crumble and CRUSH us, or worse bury us alive.