Sleep effect
From WoWWiki
Sleep effects cause a standing sleep-like state, where the character is unable to act for the duration of the ability or until dealt damage of any kind (in contrast to Stun where damage doesn't break the effect). Sleep effects are removed by the Undead ability, Will of the Forsaken.
Examples of abilities that cause sleep effect:
Various items can also cause the Sleep effect, including Slumber Sand.
Any sleep effect, no matter the duration listed, will last a maximum of 12 seconds when used against players in PvP.
Note that a Rogue's Gouge and Sap abilities, along with a Succubus's Seduction are functionally equivalent to sleep effects, that is, they prevent the target from taking any action for a certain length of time but break on damage. However, these abilities do not actually put the target to "sleep", but are considered Incapacitate and Charm effects.
See also: Crowd Control, Charm, Daze, Fear, Root, Slow, Snare, Incapacitate, Disorient and Stun.
