Dreams and nightmares are common features of sleep, but their complexity makes them a constant source of intrigue. Many theories exist for how you should interpret your dreams. The basics of how and why you dream also remain a topic of debate among scientists.

Some believe dreams have symbolic meaning or predict future events. Others see dreams as random, meaningless information. New theories suggest that dreaming helps your brain process both old memories and new information. The brain may use dreams to help you adapt to events in your life.

There is even disagreement over how to define what dreams really are. In general, you can define a dream as “a mental experience that occurs during sleep.” On a basic level dreams involve visual perceptions during sleep. These images tend to form some kind of story.

But dreaming also involves complex thoughts and emotions. Some dreams even seem to extend from sleep into wakefulness. Dreams often present an “alternate reality.” They portray events, people and places from your life. Details may be pulled from your memory. But these stories also have new information. They involve elements that are different from your life’s experience.

Measuring dreams is a challenge for researchers. Instruments can detect the parts of the brain that are active during a dream. But there is no tool that can record the dream itself. Researchers must rely on the reports that dreamers give once they are awake.

These reports tend to be imprecise. Memories of a dream can fade quickly once you are awake. At times you even may be uncertain if something was a dream or a real experience.

Some sleep disorders have features that are closely related to dreams or the act of dreaming. These “parasomnias” may involve imagery that you perceive in your mind. They also may involve actions that make an observer think you are dreaming or reacting to a dream.
Sources

_{Kryger M, Roth T, Dement W, editors. Principles and practices of sleep medicine. 4th ed. Philadelphia: Saunders; 2005.}

Lee-Chiong TL, editor. Sleep: a comprehensive handbook. Hoboken, N.J.: John Wiley & Sons; 2006.