Gamasutra - Sanity Meter in Amnesia - Evolution and obstacles.

An article by one of the designers of Amnesia: The Dark Descent, about the Sanity Mechanic. It tracks the roots and evolution of the idea, as well as the obstacles the team faced when creating the game.

http://www.gamasutra.com/view/feature/223931/game_design_deep_dive_amnesias_.php

He also mentions that he took great inspiration from this blogpost:

http://tale-of-tales.com/blog/2010/01/06/my-new-years-resolutions/