Ugh! I remember 30 years ago or so when going home really fast on slim-tyred bike because I had forgotten something. Standing up and really giving it all I had, the front wheel slipped a bit to the left and when it grapped again, my right foot was off the pedal. and my left thigh on the top tube. I had to turn right to keep my face from hitting the ground, only to then hit a tree. I ended up with a fractured pubic bone, and I still have a "bone bump" on it to this day.
Wet leaves, especially when they have started to rot are every bit as bad as ice.