When you are asleep, your defense mechanisms are down and you are psychologically more vulnerable. In other words, we shed the masks we wear in public.
Therefore what is expressed in night dreaming is probably a better representation of whom we are, not just our waking hopes and fears. Feelings and thoughts we might be unwilling to acknowledge in waking life often surface boldly in dreams.
Night dreams also speak to us in the powerful language of symbols, whereas the language of daydreams tends to be more tangible, reflecting events that have a clearer reality to them. [1]