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.
We all have had nightmares at various parts in our lives. They are quite normal. But what is exactly a nightmare and why do we have them?
Nightmares are a subcategory of dreams. The distinction of a nightmare is its frightening and/or emotional content. You tend to wake up in fear in the midst of a nightmare. Because of its frightening nature, you tend to remember your nightmares and the vivid details. They have a bigger impact upon your waking mind and its images stay with you throughout the day. One reason for nightmares may be a way of our unconscious to get our attention about a situation or problem that you have been avoiding. It is time to take notice and confront a problem or situation. Nightmares serve an important purpose in showing you what is troubling you from within you deeper levels. Discussing, analyzing, and understanding your nightmares can lead to a solution for some problem, internal conflict or personal difficulty.
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.