A nightmare is a disturbing dream associated with negative feelings, such as anxiety or fear. Nightmares are common, and occasional nightmares usually are nothing to worry about. However, they may become a problem if you have them often and they disrupt your sleep or cause you to fear going to sleep. A diagnosis of nightmare disorder is only made if nightmares cause ongoing distress or problems with daytime functioning.
Nightmares may begin in children between 3 and 6 years old and tend to decrease after about age 10. Until age 13, boys and girls appear to have nightmares in equal numbers. At age 13, nightmares seem to be more prevalent in girls than boys. Some people have them as teens or adults or throughout their lives.