But later on I found out that there is a cause - birds are causing it, by interrupting dwarves and causing multiple "vengeful joining an existing conflict..." bad thoughts, that disappear from the log after a week, yet the the resulting stress persists.
I can confirm this, my dwarft getting waay to stressed by birds....
even the squad get some trauma in station mode ....
on topic:
I made a palace room, with everything masterpiece (door, tablet, throne, cabinet, chest, engraving), and some furniture in gold with gems, and so on...
I assigned the bed it to my most stressed one, and its recovering quite fast, more or less -1k per sleep and eat.(+work)
I set the dwarf to smoth almost that I could, and asigned it to a burrow so she couldn't go outside and get more horrified and conflict emotions.
stress at:
150k - she started to yell and cry on the mayor, and got the red down sign.
250k - she started to walking obliviusly, 3 times after the walking of sorrow, she got depressed (with 265k)
now its in 244k
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I got a dwarf with a dream of master a skill, she was in 200k stress, I set she with a lot of work, and she got his legendary, wich bring down his stress to 100k +or-
my dwarfs get a lot of interested emotions, and others crappy good emotions (-8), but horrified, conflicted, and birds are WAY more stressfull