The following is explicitly to be used in emergencies for dwarves who are suddenly experiencing more stress than you're prepared for. You should still strive to generate as many happy thoughts in your fortress through other means, be they mist generators, fine furniture, legendary rooms, or all of the above.So. One of your dwarves is suddenly drowning in stress. Maybe more than one! You don't have the time to make a mist generator, and it won't even do the job as fully as you need it to be done. What's a fortress overseer to do when a dwarf is now incapable of focusing on work due to constant oblivious wandering around the halls!
The answer, my friends, is deceptively simple. Build yourself a Dwarven Sanitarium, and no, i'm not talking about a 2x2 spike execution room. I'm talking about this:
The design is pretty standard fare for managing dwarves' mental health, except it requires no mist generators, as well as only a few nice pieces of nice furniture and some engraving to increase room quality. The REAL source of happy thoughts is what you see in the back, a large hallway of dug out tunnels SPECIFICALLY for stacked engraving jobs.
To get started, carve out an entrance room or hallway as a buffer between your fort and the sanitarium, in case of tantrum. Ensure that you also have a prepared food and drink stockpile in the sanitarium, and that it is full before you seal the dwarves in. The Sanitarium should have a Great or better Bedroom and Dining room, as well as a temple to be continuously reallocated to whatever gods the depressed dwarves worship. Prayer is a big mood stabilizer as well.
The MOST IMPORTANT part of the Dwarven Sanitarium is the carving halls. In the back, dig out a 1-wide tunnel as long as you should desire, the longer the better, and jutting out from that tunnel dig out several tunnels going horizontally, with two blocks between them to allow for maximum engraving surfaces. Smooth this ENTIRE tunnel complex before beginning operation, as engraving gives better mood boosts than smoothing for your mentally ill dwarves.
Once all these steps are complete, simply make a burrow over the sanitarium, assign your mentally ill dwarves to said burrow, and unassign all labors from said dwarves aside from hauling (you never know!) and stone detailing. Designate the ENTIRE BACK AREA for engraving, and let them run loose.
It will be slow at first, as they will still be learning stone detailing from the engraving. At the very least, practicing a craft and being satisfied at work will stabilize their stress levels somewhat, as will the prayer, fine food, drink, and rooms. HOWEVER, once they reach the higher levels of stone detailing they will start creating masterpieces, and not long after that CHAIN masterpieces due to the inherent way that labors level faster the better you are at them. Enough chain masterpieces combined with the other amenities the Sanitarium provide will outright KICK all negative thoughts out of a dwarf's mind, even with the way unhappy thoughts work now, and you will be left with a completely cured, happy dwarf. Dwarves at a stress level of roughly 40,000 or greater have a chance of being unable to recover using this method, but it has so far had a 100% success rate for dwarves below that point.
The example I posted above is pretty small and meant for only one dwarf, and it's not even exactly the way I described it as I've come up with a few minor refinements since its usage. I know people have been having a lot of trouble with unhappy thoughts since 44.11 and I was hoping this contribution would help others to deal with stress, both dwarven and real.