Freud main the nation that the dream fundamentally acts as the guardian if sleep when we go to bed, the curtains are draw. The lights are turned off and in effect we are attempting to disconnect from our reality by extinguishing all external stimuli. During the night,the mind protects the sleeper from being disturbed by reacting to further external stimuli (noise,temperature,light,the need to urinate,bump arm/leg,pain,etc) as well as all internal stimuli (emotions,fears,dissatisfaction,desires,previous day's activity) by manufacturing dreams.