Our adventuring party was pretty roughed up, and my rogue had been beaten into unconsciousness. The party decides we should return to civilization to heal up. It’s a long way back to town, so the party decides to stop and rest at a well. I don’t get a vote in this because my character is unconscious, and I’m pretty much just spectating until they wake him up.
Somehow, the fighter slips and falls in the well, and as he’s covered in platemail he instantly sinks to the bottom. He begins to down.
The ranger tears off her heavy armor, shouts out “Don’t worry! I’ll save you!”, and swan dives into the well. Then she begins to drown.
The wizard sighs, and drops his quarterstaff. He carefully climbs down the edge of the well, slowly slips into the water, and… yes… he, too, begins to drown.
I should mention that this isn’t a magic well, and it’s not a well with some kind of monster pulling them under. It was just a plain old hole in the ground full of water. My party was just that bad at rolling dice.
After the rest of the group drowns the DM turns to me and says, “Congratulations! Your unconscious rogue doesn’t know it, but by not rolling a single die or engaging in any action whatsoever this session he managed to outlive the entire party.”
“Oh?” I say. “So what happens to him then?”
The DM smiles. “Well, you’re not getting any better without medical treatment, so you slowly starve to death at the edge of the well until you’re eventually found and torn apart by wild animals.”
The most lethal five minutes in my entire 15 years of gaming wasn’t even part of the adventure. The well was just a random bit of scenery the DM pulled out of the air to describe the place we happened to make camp in.