It is said that all dreams serve a purpose . While there is no agreement among scientists about why we dream, there are many ideas about the different kinds of dreams we have. One common kind of dream is the repeating dream, in which the same story is repeated again and again, often for many months or even years. Some believe these are a sign people have a problem in their life and once that problem is gone then the dream will stop. Others think _ are a way to help people remember something very important. Another well-known kind of dream is the nightmare. The pictures and stories in such dreams make people very afraid and dreamers usually remember them far more clearly than normal dreams. The cause of such dreams may be seeing something _ such as a car accident or some deadly snakes. Others think such dreams may be trying to make a person pay attention to something that is dangerous in their life. Daydreams happen during wake-time when we forget where we are or what we are doing and find ourselves in a made-up story or unreal world. We often daydream when we are doing something that is not interesting or exciting. They help us think about our future. Lucid dreams are the most fun. These happen when dreamers suddenly understand that they are dreaming. Instead of waking up, they stay in the dream and are able to control what happens in the dream as if they are making a movie. How do we know if we are lucid dreaming?
We can remember the dream very clearly. We can control what happens in the dream. We think that the dream is like a movie. We feel very nervous after we wake up.