"That is why the lower depths of the monad are so dark. Since it does not exist outside the monads that convey it, the world is included in each one of the form of perceptions or 'representatives,' present and infinitely minute elements. Still again, since the monad does not exist outside of other monads, these are minute perceptions lacing an object, that is hallucinatory microperceptions. The worlds exists only in its representatives as long as they are included in each monad.
... It is a lapping of waves, a rumour, a fog, or a mass of dancing particles of dust. It is a state of death or catalepsy, of sleep drowsiness or of numbness. It is as if the depths of every monad were made from an infinity of tiny folds (inflections) endlessly furling and unfurling in every direction, so that the monad's spontaneity resembles that of agitated sleepers who twist and turn on thier mattresses."
*quote from - Deleuze 1993, The Fold, chapter: Perception in the Folds, pg 98.