I had a fall very similar to that bout 3 summers back, though it was not so much the ladders as my footgear that was the problem.
I normally wear safety shoes for work and the weather was so hot I'd swapped them for a pair of trainers. The trainers were fine until a passing shower wet the floor and ladders. Very first climb I made after the shower resulted in a slip and the fall. I hit my head so hard it left me with a splitting headache for half an hour. Went straight home, put my safety shoes back on and have never worn trainers to work since.