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.
Dream content
Some common themes for dreams have been identified. Many people report that they have had dreams that involve one or more of these themes:
- Failing a test
- Appearing nude in public
- Having the ability to fly
- Falling
- Finding money
Yet the content of most dreams tends to depict ordinary events. Studies show that bizarre, fantastic or intense dreams are rare. Most dreams put you in a very normal situation with people you interact with on a regular basis. The dreams tend to simulate your everyday life. Most dream content involves the general concerns you have when you are awake.
Studies show that childhood dreams change as children get older. Children under the age of five recall very few dreams. Animals often play a central role in the dreams these children do report.
Children over the age of five begin to describe more dreams. Older children and teens begin to dream less about family members. By the time children approach the teen years their dreams are much like those of adults. Dreams then change little during the adult years and old age.
Disturbing dreams
Sometimes dreams involve highly emotional content that disturbs the dreamer. Fear is the most common emotion involved. But these dreams also may involve anger, disgust, embarrassment, or other negative feelings.
These are some of the most common themes of bad dreams:
- Being in danger
- Being alone or trapped
- Facing natural forces
These dreams are disturbing because they seem real. They tend to become more intense as they unfold. The memory of a bad dream can bother you as you go about your day.
A bad dream that causes you to wake from your sleep is called a “nightmare.” A nightmare disorder may develop if you have repeated nightmares that cause emotional distress. Nightmares almost always occur during rapid eye movement (REM) sleep, or “stage R sleep.”
Research shows that ongoing nightmares can have negative health effects. Studies have linked nightmares to these problems:
- Disturbed sleep
- Sleep avoidance
- Daytime anxiety
- Depression
- Suicide
Like other dreams, nightmares tend to reflect your daytime concerns. They occur more often when life events cause you to feel anxious or stressed. Nightmares often occur as a result of a traumatic event. In the dream you may experience the traumatic event all over again.
Nightmares are more common in children. Women also are more likely to report them than men. It is unclear if men have fewer nightmares, or if they simply recall and describe them less.
Dreams and stage R sleep
In general researchers believe that most dreams occur during stage R sleep. This tends to be the final stage of the sleep cycle in normal adult sleep. Each complete cycle lasts about 90 to 110 minutes. Most adults will go through four to six cycles in a full night of sleep.
Your first cycle of the night may contain only a few minutes of stage R sleep. Your R sleep then tends to get longer during each of the following sleep cycles. In a full eight hours of sleep, about two hours are spent in stage R sleep.
Your brain’s activity changes as your body repeatedly goes through each of the sleep stages during the night. Brain waves are slow during the stages of deep, non-REM sleep (N sleep). Entire regions of your brain remain inactive during these stages.
You are less likely to recall having a dream when you wake up from N sleep. This may mean that you dream less during this part of the sleep period. Or it could mean that you remember less of what you dream during N sleep.
In contrast your brain waves are much faster and active during stage R sleep. Some regions of the brain are reactivated. This activity is reflected in your dreams. Dreams during stage R sleep tend to be more vivid, emotional and bizarre than dreams during N sleep.
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.
More Information
What does it mean when I have the same dream over and over again?
What does it mean if I don’t dream at all?
If I have frequent nightmares does it mean that I’m crazy?
Why does my husband seem to act out his dreams in his sleep?
Do animals dream like people do?
Reviewed by David Kuhlmann, MD
Updated July 10, 2007
