I had a lot of ‼FUN‼ last night.
First, there was a goblin siege. A marksdwarf got shot and killed, and some pets also died. No tantrumming that I saw, but there was some unhappiness among his friends. Then came a mysterious fire in an aboveground meeting area. Several dwarves were killed, and that's when the real shit hit the fan. The dwarves had a lot of free time, so they got to know each other well, and those deaths made a lot of dwarves very unhappy and even miserable. Tantrums started flying, dwarves were murdered, and I wrongfully accused a dead animal and a dwarf as the murderers of the first couple dwarves. It went down hill from there, and the entire population helped turn the fortress into their own little slice of hell. A lot of dwarves went berserk and the guardsmen were handing out beatings left and right. Must have been thirty or more dwarves that went melancholy or SRM. I tried locking a lot of them, and some of the berserkers, in their bedrooms or hospital rooms, but by that point the damage had already been done. And somehow the dwarves became aware of one anothers' deaths from behind locked doors several times. No idea what was up with that.
So far, the population dropped from ~135 to ~65, and there are plenty of wackjobs waiting to starve to death, and as many dwarves waiting to lose their own minds. I spotted a few dwarves that aren't currently unhappy, though, so I guess there's still hope.