I think tantrum spirals are MUCH more rare and unlikely to occur than generally thought. I've had awful disasters strike my fortresses... like HFS accidents killing 2/3 of the population... and a few dwarves will sometimes tantrum briefly, a couple may get melancholy and commit suicide, but as a whole the remaining population seems to get over it fairly quickly.
My super tantrum spiral was a series of unfortunate events.
First off I recieved gigantic immigrant waves so I didn't have housing for everyone or enough dining rooms.
Secondly I completely ignored mandates that my nobles ordered, thinking they wouldn't punish my exports - and a number of dwarves were executed for this.
Thirdly a number of dwarves were murdered by goblins. I think they were 3 soldiers and 2 civilians.
Fourth. The tantruming started - the nobles did most of it at first. They are "above" the law and they were very upset about some stupid shit like "a lesser's pretentious bedroom arrangements" which I don't even know how to fix. and they hit people.
Fifth. Everyone who tantrumed and started fights would get immediately punished by the guards - causing executions and beatings to skyrocket, the zoo was destroyed and wild animals (undead and not) attacked the dwarves causing further horrible thoughts.
Sixth. Over 20 dwarves went berzerk. Most were put down immediately but one of them went on a murder spree that caused the life of 5 men and some animals.
... I don't have alot of experience with tantrum spirals but it doesn't seem to be just ONE disaster that sets it off. it needs to be fueled to keep going