Daily life experiences don’t always present themselves in dreams immediately. Sometimes an experience from life will filter through to a dream after several days or even a week. This delay is what’s known as <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3202556/">dream lag</a>. Dreaming of these events—and the timing by which memories appear in dreams—may actually be an <a href="http://www.ncbi.nlm.nih.gov/pubmed/15560767">important part</a> of the memory consolidation process.

Dream lag

Research indicates that a majority of dreams contain content related to <a href="http://www.ncbi.nlm.nih.gov/pubmed/24635722">autobiographical memories</a>—memories about the self—as opposed to episodic memories, which deal with events and details such as locations and times.

Dreams about self

Nightmares are broadly defined as frightening dreams that result in some degree of awakening from sleep. Nightmares themselves contribute to disrupted sleep not only by waking the sleeper but also because they can lead to fear of falling asleep and returning to a disturbing dream. According to research, nightmares may contribute to insomnia, daytime fatigue, depression, and anxiety.

Nightmares

Another function of dreaming appears to be processing and coming to terms with traumatic events. Grief, fear, loss, abandonment, even physical pain are all emotions and experiences that often replay themselves in dreams.

Processing traumatic events

Night terrors are very intense episodes of fright during dreams. These frightening episodes are often accompanied by screaming or yelling, as well as by physical movement such as leaping out of bed or flailing in panic. Research suggests that sleep terrors occur during non-REM sleep dreaming, while nightmares tend to happen during REM sleep.

Night terrors

Recurring dreams are dreams that re-appear with some pattern of regularity. Studies suggest that recurring dreams may contain more threatening<a href="http://www.ncbi.nlm.nih.gov/pubmed/16720254"></a> content than regular dreams. Research suggests links between recurring dreams and psychological distress<a href="http://www.ncbi.nlm.nih.gov/pubmed/24976740"></a> in both adults and children.

Recurring dreams

In lucid dreams, the dreamer is aware of the fact that he or she is dreaming, and often can manipulate or control the dream as it unfolds. Studies have found that lucid dreamers displayed <a href="http://www.ncbi.nlm.nih.gov/pubmed/19750924">significantly higher</a> brain wave frequencies than non-lucid dreamers, as well as <a href="http://www.smrv-journal.com/article/S1087-0792(14)00068-9/abstract">increased activity</a> in parts of the frontal lobe.

Lucid dreams

Dreams appear to be influenced by our waking lives in many ways. Theories about why we dream include those that suggest dreaming is a means by which the brain processes emotions, stimuli, memories, and information that's been absorbed throughout the waking day.

Nightmares

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