Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

Fiendish Resilience (Su): Beginning at 8th level, a warlock knows the trick of fiendish resilience. Once per day, as a free action, he can enter a state that lasts for 2 minutes. While in this state, the warlock gains fast healing 1.

At 13th level, a warlock's fiendish resilience improves. When in his fiendish resilience state, he gains fast healing 2 instead. At 18th level, a warlock's fiendish resilience improves to fast healing 5.

Supernatural Abilities (Su)
Supernatural abilities are magical and go away in an antimagic field but are not subject to spell resistance, counterspells, or to being dispelled by dispel magic. Using a supernatural ability is a standard action unless noted otherwise. Supernatural abilities may have a use limit or be usable at will, just like spell-like abilities. However, supernatural abilities do not provoke attacks of opportunity and never require Concentration checks. Unless otherwise noted, a supernatural ability has an effective caster level equal to the creature’s Hit Dice.

This question should actually be directed to dm team.