The most interesting field of dream experience and research is the Lucid dream. A very sensitive state of consciousness that differs from the ordinary dream state. The Lucid dream is a dream where one is aware that one is asleep and dreaming and has full volitional control within the dream. Most people occasionally remember their dreams, though again, many people say they never dream. Reasearch has shown that almost everybody dreams with the exception of people taking various drugs or medications and people with rare sleeping disorders. The average person has between 2 and 5 dream periods throughout the sleep cycle and the dream period increases with time, so the dreams become longer the longer the person sleeps and it is usually later in the sequence that the lucid state arises although again there are exceptions and adepts are available to enter the lucid state more or less easily. Carlos Castenada describes how the girls in the group were able to enter a dream world almost immediately upon falling asleep.