I just received an email from a friend who doesn't realize that she is being gaslighted by her eldest (adult) child. So that makes me think I should touch on this subject here because it is a form of psychological abuse that narcissists often employ.
For a brief article on the subject of gaslighting with excellent examples of how this tactic is employed, click here. Gaslighting occurs when a person you trust to tell you the truth about reality, is, in fact, bending reality with lies. When this happens consistently over a period of time it causes you to question your sanity.
In the fifth season of the TV series "24" we see gaslighting in the relationship of President Logan with his wife. Because he is now the most powerful man in the world, his version of reality holds even more sway over her. He can recruit a powerful cadre of support for any and all versions of "reality" he decides to concoct. Mrs. Logan finds herself isolated psychologically because no one will validate the reality she is perceiving with her own senses. And when she becomes very inconvenient by insisting on her perception of reality, he threatens her with commitment to a loony bin. It is a particularly graphic and ugly illustration of this powerful form of psychological control and abuse.
If you find yourself often questioning your own sanity you need to suspect you are being gaslighted. In the absence of any who will support what you are seeing, hearing, and knowing, please give yourself permission to believe yourself. Gaslighting is a deliberate and evil tactic. So when you've determined that someone is doing this to you, it is past time to remove yourself from this person's sphere of influence.
Wikipedia has a brief entry on gaslighting.