no sex and violence are the most common in dreams because these are the strongest most primative and most resticted actions and feelings common amoungst all humans. this area of the brain Freud identified as the I.D or inner desires.
all dream messages are unique to the dreams and only the dreamer can properlt interpret them.
and no one forgets anything. everything we see hear smell taste touch and feel is stored in the unconscious. remembering it is often uncontrolled and we remember different things at different times. alot of things, we as emotional beings block out and choose not to recall because they are trumatic, painful or irrelavent.
although with alot of mental discaplin and training through meditation and other mental training we can chose to recall on demand.