Monsters (and you!) can be put to sleep by a number of different means:
- The "sleep" brand (unique to needles)
- Ensorcelled Hibernation and Metabolic Englaciation
- The monster-only "sleep" spell/effect, usable by The Enchantress and Aizul.
Monsters are usually asleep at the time that they are generated (or "dormant", if incapable of sleep), and tend to fall asleep again if enough time has passed since they last encountered the player.
The player character will always wake if he/she takes any amount of damage.