Insanity causes a dwarf to immediately stop what they were doing and go mad, rendering them useless as they refuse to follow orders or perform any job. They also stop eating, drinking and even sleeping. Insanity comes in three flavors: melancholy, stark raving mad and berserk.
The effect is permanent and there is no current way to cure them. Insanity always ends in the death of the afflicted dwarf, whether by suicide or homicide, which will upset their friends and family. This can lead to a vicious circle of depression and tantrums. Make sure to build coffins to avoid compounded unhappiness from their friends decaying on open air.
Certain events/conditions can drive a dwarf insane. It is not possible to force insanity, only to foster its growth.
- Entering a strange mood but failing to complete a legendary artifact.
- Being very unhappy or miserable for a long time. Unlike a failed mood, this is not a guaranteed insanity, and dwarves can remain unhappy for many months without snapping.
- Diplomats and merchants who are trapped inside your fortress for a long time will also go insane, even though you do not technically "own" them. This includes their pack animals used to haul the goods. A caged diplomat will go insane immediately (e.g. if he falls unconscious while standing on cage trap)
There are three known types of insanity, but a dwarf may only be afflicted by one at a time (one is enough). The personality of the dwarf influences the type of insanity.
- Stark raving mad
- <dwarf> has gone stark raving mad!
- Running around babbling!
- Crawling around babbling!
- The afflicted will strip naked and drop each of their items one by one. They will then wander your halls aimlessly (or sometimes stick to their room), babbling incoherently until they eventually die of dehydration or starvation. They do not actively seek out their own deaths, but death does a pretty good job at finding them anyway, as they ignore any and all hazards they encounter while milling about.
- Dwarves with high anxiety are more likely to go stark raving mad.
- <dwarf> is stricken by melancholy!
- Stricken by melancholy...
- The afflicted is overcome by depression and will seek out ways to end their life, considerably slowing their movement in the process. If they cannot find a cliff to jump off of or water/magma to drown/burn up in, they will simply starve themselves to death. Be warned that a melancholy mother may take her baby's life with her own if she still carries it.
- Dwarves with high depression are more likely to be stricken by melancholy.
- <dwarf> has gone berserk!
- In a berserk rage!
- The afflicted attacks friend and foe alike in a blind rage. This can be dangerous if it happens to an experienced dwarf (especially one carrying an artifact weapon). Luckily, war dogs can quickly bring down an unskilled dwarf.
- Berserk dwarves have also been reported to pull every lever they can find. This may be a mere annoyance or very fun, depending on your fortress' design.
- The dwarf in question becomes an enemy to your civilization, meaning it will set off traps and engage your military.
- Dwarves with high anger are more likely to go berserk.
 Dealing with insanity
As stated, there is no cure for the insane. But there are ways you can deal with dwarf quickly and efficiently which can have little impact on your fort's health. Of course, that isn't always as fun.
- Lock the door or otherwise seal them in
- Insane dwarves - even the berserk kind - cannot get by a locked door. If your insane or soon-to-be-insane dwarf is in a lockable room, just lock the door; you can then wait for them to starve themselves to death. Even if your workshops aren't in rooms on their own, you'll have a month or two while your dwarf stands in their workshop waiting for the items they need. You can use that time to build a wall around the workshop and seal the dwarf in. (Indeed, it may be a good idea to start doing this instinctively as soon as a dwarf claims a workshop, or dig 3x3 squares with only one way in for your workshops so you can build a door in the gap and lock it as soon as the dwarf goes mad.)
- Station your military around them
- If you suspect a dwarf is about to go insane, whether from misery or a failed mood, you can station a squad of soldiers by them
- This is a decisive solution to dealing with a berserk dwarf. Better they charge into an axe than an unlucky mason walking along.
- Make sure you have a cliff and that the bottom is accessible
- As cruel as it might sound, making sure your melancholy dwarves have a place to jump off of provides a quick and easy death instead of waiting for them to eventually starve. If you're able to access the bottom of the cliff you can more quickly bury the corpse and recover the deceased's items.
- Assign wardogs to a potential case, or to those around them
- Similar to military, wardogs will recognize the insane as an enemy, and rip them apart the moment they become a danger. This tends to only work with the more violent types. One or two is enough for a non-wrestler, and has the advantage of following the dwarf wherever they go.
- Post cage traps
- Posting a cage trap near a dwarf thats about to go berserk will imprison him in a cage and prevent a needless death. he can be kept alive in this cage indefinitely and it will keep your other dwarves from having a bad thought relation to the would-be death of their friend/husband/whatever. If you're concerned about the security of a control room, a cage trap outside will stop any mad lever puller before they can do any damage.
 Insanity in Adventure Mode
In Adventure Mode, it is possible to have your adventurer become melancholic, this can be caused by extreme drowsiness. When this happens, your adventurer will be able to fall off cliffs without using the ALT-key, and possibly won't be able to swim during this state. Other than that, nothing really else happens, and the effect goes away when you travel on the world map.