Sleep
From DwarfFortressWiki
Dwarves sleep approximately every month and a half (6 weeks), and will sleep for 1-2 weeks. They prefer to sleep indoors, on a bed, in their own room, and the quality or roughness of the item or surface they are resting on will have an impact on their happiness when they awaken. The restfulness of their sleep also has an impact on their happiness, and depends upon where they are sleeping and whether or not there is any noise reaching them.
A sleeping dwarf flashes between their standard icon and Z.
In versionv0.27.176.38c, sleeping creatures can block attacks without waking up! This has been fixed in the next version.
Starting in versionv0.28.181.39a, sleeping dwarves are marked as being unconscious. It should also be noted that traps will activate for any unconscious entity. This combination has the potential to be very dangerous, very useful, and/or very amusing.
