Rapid Eye Movement (REM) sleep

REM or Rapid Eye Movement is the period of deep sleep where the eye moves rapidly. It is considered a part of the human sleep cycle. It recurs cyclically several times during a normal period of sleep and characterized by increased neuronal activity of the forebrain and midbrain, by depressed muscle tone. This is the stage where dreaming takes place and accounts for roughly 20% of a full night of sleep.