Why do we have dreams at night-time? what is it for?

Brain Processing: Our dreams are essentially our brain's way of processing information it has collected over the short term. We have dreams during a certain phase of sleep called rapid eye movement; we have about 4 REM cycles per night (if you have a normal 7-8 hour sleep period). It is important that we dream, as this is partly what helps us awaken feeling rested and refreshed. People who sleep, but don't dream enough, will not feel like they are getting enough rest.

No one knows: We don't really know for sure why we dream. Recent evidence suggests that dreaming sleep (rem sleep) is involved in memory consolidation and learning. Freud thought that dreams were disguised wish fulfillments. Whether this is the case or not, most psychoanalysts still believe that dreams are, like freud said, the "royal road to the unconscious.".