It's the natural progression through stress. It comes right after "has been under a great deal of stress" and right before "has been utterly harrowed by the nightmare that is his tragic life."
It seems anyone with either haggard or harrowed just needs to be consigned to the magma. Nothing fixes them.
Yes, nothing fixes them. It is still surprising it comes so fast after first "great deal of stress". Specially now, to Dwarves, whom neither are depressive nor had any rain encounters recently. This is odd. I did not figured out what causes that particular down-spiral. For now it looks like every year 1-5 Dwarves just has to go crazy.
Some temporarily, some permanently. For no obvious reason.
I do not think anything fixes regular depression either. Not only haggard or harrowed. Even with disabled hauling already on "great deal of stress".
When these Dwarves start loosing time to mental illness, then they are basically done.
This part mechanic is very simple. Some of those major needs from locations, just simply take too long to satisfy.
Positive effects are entirely gone by 2 month. Locations give these issues, as the activities at locations simply take too long time to perform.
All positive effects pass (specially in adventure mode) away too fast.
I also noticed with 13 different types of alcohol now, that none Dwarf ever gets euphoric.
Even Dwarves, who drink alcohol, which they prefer to "consume", get mood "content".
I put my alcohol stockpile in temple to get Dwarves to pray frequently (easier to satisfy then friends&family). I wonder, if this is some issue.