Dreams may have an important physiological function

According to Dr J. Allan Hobson, the major function of the rapid eye movement (REM) sleep associated with dreams is physiological rather than psychological. During REM sleep the brain is activated and "warming its circuits" and is anticipating the sights, sounds and emotions of the waking state.

Dr Hobson said the idea explains a lot, and likened it to jogging. The body does not remember every step of a jog, but it knows it has exercised, and in the same way we do not remember many of our dreams, but our minds have been tuned for conscious awareness.

Unimatrix Zero

Though you can scarcely tell by the trailers, UNIMATRIX ZERO Episodes: 1 &  2 was part of the series, 'STAR TREK VOYAGER'. It dealt with the ominous species known as 'THE BORG' and what occurred during their sleep states (regeneration cycles). Only 1 in every million humanoids assimilated by THE BORG were capable of entering a dream reality where they could interact and form new lives away from the hive. There, these unique individuals plot a rebellion against the collective, which results in harrowing assimilation for various crew members of 'VOYAGER'. I was never a big fan of 'VOYAGER' but pretty much anything in the TREK universe that involves THE BORG, or the mischevious entity known as Q, is worth a look...