The Fog of Eternity is a term applied to the mental confusion resulting in a vampire's mind that has gone through a long-term torpor.
As a Kindred sleeps in torpor, their dreams and memories collide with hallucinations and visions of past (and even future) events inside their head, making their actual memory of events in their life and unlife extremely unreliable. The longer the torpor, the less reliable those memories become. The Fog of Eternity has been described as "a decades-long waking dream" and "a protracted nightmare." 
- ↑ , p 39