Dreams - From Wikipedia
A 'dream' is the experience of a sequence of images, sounds, ideas, emotions, or other sensations during sleep, especially REM sleep. The events of dreams are often impossible or unlikely to occur in physical reality, and are outside the control of the dreamer. The exception to this is known as lucid dreaming, in which dreamers realize that they are dreaming, and are sometimes capable of changing their dream environment and controlling various aspects of the dream. The dream environment is often much more realistic in a lucid dream, and the senses heightened.
+ Neurology of dreams
There is no universally agreed-upon biological definition of dreaming. General observation shows that dreams are strongly associated with REM sleep. REM sleep is the state of sleep in which brain activity is most like wakefulness, which is why many researchers believe this is when dreams are strongest, although it could also mean that this is a state from which dreams are most easily remembered. During a typical lifespan, a human spends a total of about six years dreaming. (which is about 2 hours each night. It is unknown where in the brain dreams originate — if there is such a single location — or why dreams occur at all.
+ Cultural history
Dreams have a long history both as a subject of conjecture and as a source of inspiration. Throughout their history, people have sought meaning in dreams. They have been described physiologically as a response to neural processes during sleep, psychologically as reflections of the subconscious, and spiritually as messages from God or predictions of the future.
Oneiromancy deals with the use of dreams for divination. In ancient Judeo-Christianity: in the Tanakh, Jacob, Joseph and Daniel are given the ability to interpret dreams by Yahweh; in the New Testament, divine inspiration comes as a dream to Saint Joseph, the husband of Mary, when the Angel Gabriel spoke to him in a dream and told him that the baby Mary was carrying was the Son of God. After the visit of the Three Wise Men to them in Bethlehem, an angel appeared to him and told him to take Mary and Jesus to Egypt for their safety. The angel appeared again in a dream to tell him when it was safe to return to Israel. The story of Saint Patrick and his conversion of the people of Ireland also features dreaming. When Patrick was enslaved in Antrim he was told by God in a dream that there was a boat waiting in Wicklow to bring him back to his homeland.
Dreams were thought to be part of a spiritual world, and were seen as messages from the gods. Likewise, the Torah (known in Christianity as the first five books of the Old Testament) and the Qur'ān tell the same story of Joseph, who was given the power to interpret dreams and act accordingly. Biblical stories and actions that came from dreams (and visions) form about one-third of the entire Bible (383 References to "Dream" "Vision" and "Seer" / 74 times alone for "Dream" in the King James Bible: Gen 20:3; Gen 31:10; Gen 31:11; Gen 31:21; Gen 37:5 etc). Many cultures practiced dream incubation, with the intention of cultivating dreams that were prophetic or contained messages from the divine. In Islam, good dreams are considered to be from Allah and bad dreams from Satan .In India, scholars such as Charaka (300 BC) gave alternative explanations for the reasons behind dream. In Charaka Samhita the explanation of dreams is as follows : " The cause of dream are seven. They are what you have seen, heard, experienced, wish to experience, forced to experience, imagined and by the inherent nature of the body".
The belief that dreams were part of a spiritual world continued into the Early Middle Ages. A story from Nevers, which is reproduced in the Golden Legend, states that one night the Emperor Charlemagne dreamed that he was saved from being killed by a wild boar during a hunt by the appearance of a child, who had promised to save the emperor from death if he would give him clothes to cover his nakedness. The bishop of Nevers interpreted this dream to mean that he wanted the emperor to repair the roof of the cathedral dedicated to the boy-saint Saint Cyricus.
+ Dream content
From the 1940s to 1985, Calvin S. Hall collected more than 50,000 dream reports at Western Reserve University. In 1966 Hall and Van De Castle published The content analysis of dreams in which they outlined a coding system to study 1,000 dream reports from college students. It was found that people all over the world dream of mostly the same things. Hall's complete dream reports became publicly available in the mid-1990s by Hall's protégé William Domhoff allowing further content analysis.
The most common emotion experienced in dreams was anxiety. Negative emotions are more common than positive feelings. Some ethnic groups like the Yir Yiront showed an abnormally high percentage of dreams of an aggressive nature. The U.S. ranks the highest amongst industrialized nations for aggression in dreams with 50 percent of U.S. males reporting aggression in dreams, compared to 32 percent for Dutch men.
+ Gender differences
In men's dreams 70 percent of the characters are other men, while a female's dreams contain an equal number of men and women.  Men generally had more aggressive feelings in their dreams than women, and children's dreams did not have very much aggression until they reached teen age. These findings parallel much of the current research on gender and gender role comparisons in aggressive behavior. Rather than showing a complementary or compensatory aggressive style, this study supports the view that there is a continuity between our conscious and unconscious styles and personalities.
+ Sexual content
Sexual content is not as prevalent in dreams as one might expect. The Hall data analysis shows that sexual dreams show up no more than 10 percent of the time and are more prevalent in young to mid teens.
+ Recurring dreams
While the content of most dreams is dreamt only once, most people experience recurring dreams—that is, the same dream narrative is experienced over different occasions of sleep. Up to 70% of females and 65% of males report recurrent dreams.
+ Common themes
Content-analysis studies scientists have identified recurring themes in dreams. Common reported themes have been shown to be: themes relating to school, being chased, sexual experiences, falling, arriving too late, a person now alive being dead, flying, and failing an examination. 12% of people dream only in black and white. 
+ Understanding dreams
* Psychodynamic interpretation of dreams
Both Sigmund Freud and Carl Jung identify dreams as an interaction between the unconscious and the conscious. They also assert together that the unconscious is the dominant force of the dream, and in dreams it conveys its own mental activity to the perceptive faculty. While Freud felt that there was an active censorship against the unconscious even during sleep, Jung argued that the dream's bizarre quality is an efficient language, comparable to poetry and uniquely capable of revealing the underlying meaning. Fritz Perls presented his theory of dreams following the holistic nature of gestalt therapy. Dreams are seen as being projections of parts of oneself. Often these are parts that have been ignored, rejected or even suppressed. One aim of gestalt dream analysis is to accept and reintegrate these. According to Perls, the dream needs to be accepted in its own right - not broken down and analysed out of existence.
+ Other associated phenomena
* Lucid dreaming
Lucid dreaming is the conscious perception of one's state while dreaming. The occurrence of lucid dreaming has been scientifically verified.
* Dreams of absent-minded transgression
Dreams of absent-minded transgression (DAMT) are dreams wherein the dreamer absentmindedly performs an action that he or she has been trying to stop (one classic example is of a quitting smoker having dreams of lighting a cigarette). Subjects who have had DAMT have reported awaking with intense feelings of guilt. Some studies have shown that DAMT are positively related with successfully stopping the behaviour, when compared to control subjects who did not experience these dreams.
* Dreaming as a skeptical argument
While one dreams a non-lucid dream, one will not realize one is dreaming (one classic example is a child dreaming that they are using the toilet and end up wetting the bed because they don't realize that they are in a dream). This has led philosophers to the idea that one could be dreaming right now (or at least one cannot be certain that one is not dreaming). First formally introduced by Zhuangzi and popularized by Hindu beliefs, the dream argument has become one of the most popular skeptical hypotheses. Out of the major religions and philosophies in the world, Buddhism makes most use of this argument.
* Recalling dreams
According to Craig Hamilton-Parker,  author of Fantasy Dreaming, many humans find certain dreams extremely difficult to recall. According to David Koulack in "To Catch A Dream," researchers refer to these types of dreams as "no content dream reports." It is thought that such dreams are characterized by relatively little affect. According to Koulack, factors such as salience, arousal and interference play a role in dream recall and dream recall failure. According to Henry Reed, author of Dream Medicine, a useful technique to improve dream recall is to keep a dream journal. Stephen LaBerge, author of Exploring the World of Lucid Dreaming, also suggests that one must lie perfectly still upon awaking from a dream, not letting concerns of the day occupy the mind. It is quite common to not remember much of what has just been dreamed, but LaBerge maintains that with sufficient concentration, the entire dream may be recalled.
Another sufficient method to recall a dream is to wake at least 5 minutes after dreaming.
* Déjà vu
The theory of déjà vu dealing with dreams indicates that the feeling of having previously seen or experienced something could be attributed to having dreamt about a similar situation or place, and forgetting about it until one seems to be mysteriously reminded of the situation or place while awake.