Sleeping creatures result from the use of the sleep spell or from the death of a wizard. If a sleeping creature is not awakened within a certain time it will decay and disappear (leaving no corpse). If you have a wake spell, a sleeping creature can be awakened, and will then swear allegiance to your wizard.
Sleeping creatures cannot move or partake in combat, but can be attacked by other creatures. Note though, that you can never get engaged to a sleeping creature. The shadow wood will not attack sleeping creatures.
Other objects such as fire, gooey blob, and walls can also go into a sleeping state. In this state fire and gooey blob stop growing and other objects stop repairing themselves. The sleep spell, however, can only be used on creatures.
A sleeping creature can be cloaked. Once awakened the cloak will remain intact and function as expected. There is a slight risk for the user of the wake spell in that you cannot necessarily know in advance what you are waking up.
A sleeping creature appears just like its living counterparts on the board.