They mean your unconscious mind is processing information of an experience or thought (gained from an experience usually) from your conscious mind from that day, from some previous day or event, that might be important or you haven't made sense of, or from something that may be worrying you.
ok then well wot happens when u have a dream that makes no sense whatsoever? eg. a dream about completely random events that u werent even thinking about?????
Not sure if this is true but i read somewhere that you hav about 6 dreams every night and that if you don't sleep one night you hav more dreams when you eventually do sleep to make up for it?? It's weird coz I hardly ever remember my dreams so don't normally give it much thought...