What, then, is that incalculable feeling that deprives the mind of the sleep necessary to life?
A world that can be explained even with bad reasons is a familiar world. But, on the other hand, in a universe suddenly divested of illusions and lights, man feels an alien, a stranger. His exile is without remedy since he is deprived of the memory of a lost home or the hope of a promised land.
This divorce between man and his life, the actor and his setting, is properly the feeling of absurdity.

At this point of his effort man stands face to face with the irrational. He feels within him his longing for happiness and for reason.The absurd is born of this confrontation between the human need and the unreasonable silence of the world. This must not be forgotten. This must be clung to because the whole consequence of a life can depend on it. The irrational, the human nostalgia, and the absurd that is born of their encounter — these are the three characters in the drama that must necessarily end with all the logic of which an existence is capable.

-- Albert Camus, An absurd reasoning (From The myth of Sisyphus)