they talk about "daydreaming". While daydreaming has long been derided as a lazy, non-productive pastime, it is now commonly acknowledged that daydreaming can be constructive in some contexts. There are numerous examples of people in creative or artistic careers, such as composers, novelists and filmmakers, developing new ideas through daydreaming. Similarly, research scientists, mathematicians and physicists have developed new ideas by daydreaming about their subject areas. Hallucination A hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are perceptions in a conscious and awake state, in the absence of external stimuli, and have qualities of real perception, in that they are vivid, substantial, and located in external objective space. The latter definition distinguishes hallucinations from the related phenomena of dreaming, which does not involve wakefulness. Nightmare A nightmare is an unpleasant dream that can cause a strong negative emotional response from the mind, typically fear or horror, but also despair, anxiety and great sadness. The dream may contain situations of danger, discomfort, psychological or physical terror. Sufferers usually awaken in a state of distress and may be unable to return to sleep for a prolonged period of time. Night terror A night terror, also known as a sleep terror or pavor nocturnus, is a parasomnia disorder that predominantly affects children, causing feelings of terror or dread. Night terrors should not be confused with nightmares, which are bad dreams that cause the feeling of horror or fear. Déjà vu One theory of déjà vu attributes the feeling of having previously seen or experienced something to having dreamed about a similar situation or place, and forgetting about it until one seems to be mysteriously reminded of the situation or the place while awake. See also Dream dictionary Dream incubation Dream of Macsen Wledig Dream pop Dream sequence Dream yoga Dreamcatcher Dreamwork False awakening Hatsuyume Incubus Lilith, a Sumerian dream demoness List of dream diaries Mare (folklore) Mabinogion Sleep in animals Sleep paralysis Spirit spouse Succubus Works based on dreams References Further reading Dreaming (journal) Harris, William V. (2009) Dreams and Еxperience in Classical Antiquity. Cambridge, MA & London: Harvard University Press. External links Archive for Research in Archetypal Symbolism website The International Association for the Study of Dreams alt.dreams A long-running USENET forum wherein readers post and analyze dreams LSDBase – online sleep research database documenting physiological effects of