I have just experienced my first tantrum spiral. As a new DF player of about a week, my first successful(moderately) fortress has pretty much collapsed on itself.
It all started with, what I thought, was a successful raid defense. 4 squads of 12 goblins appeared and headed towards the entrance. As the noob I am, I have a poor defense setup, basically a bunch of stone traps with a dividing wall to stop arrows - it had worked until then, but this was twice as strong as anything that had attacked before.
I sent out two squads, 5 dwarfs strong each. Naturally, only two dwarfs are there when the first goblin squad shows up. I tried to keep them behind my traps, but one rushed out head on, and the other wasn't two far behind. Amazingly, the first takes out 3 goblins in a matter of seconds, and together they push back the others until another goblin squad shows up and rains death with arrow fire. The goblins start to push through my choke point, and many are hurt from falling rocks, then the rest of my army shows up and the real fight begins.
The whole time the battle is going on, stupid civilian dwarfs keep trying to run in and pick up stuff that's been dropped, resulting in a few unnecessary deaths. But in the end, my army drives them off with minimal causalities, and things seem ok. Total losses, 3 soldiers, 3-4 workers.
So, I think things are getting back to normal when next thing I know I have dwarfs starting to tantrum. Turns out that one of the dwarfs killed was a child, now his parents and all his friends are pissed. After the first round of tantruming the whole fort is flashing red. Dwarfs start berserking, bodies start flying, and blood ends up all of the dining room floor. This goes on a few times with most dwarfs making it out unharmed. Then a legendary fish cleaner goes berserk. He takes out 3 dwarfs before guards can make it to him, then proceeds to mangle the swordsdwarf and elite wrestler that are first on the scene. He then murders a child, then a baby, and causes unknown causalities as he makes it into the dining room before finally being taken down.
At that point I might as well have ended it. Blood was spattered all of the dining room. Bodies lay strewn from the manufacturing quarters to the great dining hall, and only more pain and sorrow was to come.
To make a long story short, I now stand at 60 dwarfs and I fully expect at least another 10 to die from blood loss, thirst, hunger, or plain misery since at least that many lie on the floor helpless, as other dwarfs pass them without batting an eye. Already countless have suffered the same fate.
Oh, and as I finish writing this, the nobles I've been awaiting for nearly two years have finally shown up. I've been sitting at 130+ dwarfs, 500k+ imports and 10k+ exports for two years, slaughtering any meager assault attempted, only to be told that they were all were too scared to make the journy despite only two deaths the entire time. Now, they're happy to walk in the fortress passed dead and dying bodies, blood covered everything, and every dwarf they see more pissed off than the last. I wouldn't be surprised if one of them gets murdered soon after they enter the dining room.