At almost the same time your friend was falling into the sewer I fell into a thermal hot springs or geyser in Yellowstone NP. I was crossing a very large meadow with three other fellas, going to fly fish the Gibbon River. We were about two miles below the Norris Geyser Basin, as I recall.
I mentioned to everyone that the ground was getting very, very swampy and spongy. As soon as I had said that I broke through the surface ground, and plunged into a hot springs/geyser/sinkhole---or whatever the bloody thing was called. The hole was probably three and half to four feet in diameter, I think.
Luckily I fell forward when the ground collapsed and my chest landed on the front of the hole and my arms were on the side of the hole. I couldn't tell for sure if my legs and feet were in the water because I was wearing heavy neoprene waders and sturdy wading boots. But, by the time my friends pulled me out my feet were definitely warmer---but that could have been from the heat and steam (?) in the hole.
We were all lucky that the ground my friends were standing on did not collapse also. Someone had a small flashlight and we estimated the water to be about five or six feet below the surface ground, and there was no telling how deep the water was.
I had left my SLR in the car, and was carrying a small digital point and shoot pocket camera. I would have ruined my SLR, and my chest, if I had been wearing it when I fell chest first onto the side of the hole. I apparently had dropped my rod on the ground when I fell and it was undamaged, so it was a rather lucky day, all things considered.
I just realized that this thread asked for problems from this year so I will just admit that in August I left my GPS on the fender or bumper of my car at a trailhead parking lot and drove away with it on the fender/bumper. It fell off and I've searched and searched and never found it. What is completely embarrassing is that a month earlier I had done the same thing with my hiking staff. Maybe it is true old guys get forgetful but in both cases I was distracted by weather and active kids.