The very first time I dug too deep and unleashed HFS. I was playing with candy gleefully and by the time I realized my error, it was far too late. I rapidly barricaded parts of the fortress off to try and save as much as possible (I lost 1/3 of my 180 dwarves straight away). I managed to wall off the upper part of my fort, and the last part to save was my magma forge / metal industry area. Inside was a handful of dwarves, my sheriff, and a couple of children.
I quickly turned off all of their jobs and gave all of them masonry. In fact I did that for pretty much the entire fort, because I needed walls built /yesterday/, but these guys were trapped. I set the walls to build and realized they were all asleep. There's fire breathing clowns hosing down the fort 3 z-levels above and there's 5 panels of wall that need to be built to save this and EVERYONE is asleep. Really? So finally a couple of them wake up long enough to build the walls and they're successful in doing so, except for one last panel which the dwarf goes to sleep WHILE CARRYING THE ROCK to build it. Unbelievable. I'm gonna lose my entire metal industry because one panel of wall won't get sealed up. Meanwhile, watching all of this, is my Sheriff. He's done exactly nothing because he's furious. I think he lost his family to the clowns or something because he's a cross word away from flying into a tantrum. Much to my surprise, he picks up a rock when that other dwarf falls asleep, and builds the last wall part. In doing so, he ends up on the wrong side of the wall and dies to the clowns. The livid, uber mad, Sheriff winds up being a hero and saving the day while the rest of the dwarves take a nap and hope everything works out for the better.