A nightmare, also known as a bad dream,[1] is an unpleasant dream that can cause a strong emotional response from the mind, typically fear but also despair, anxiety or great sadness. However, psychological nomenclature differentiates between nightmares and bad dreams; specifically, people remain asleep during bad dreams, whereas nightmares can awaken individuals. The dream may contain situations of discomfort, psychological or physical terror, or panic. After a nightmare, a person will often awaken in a state of distress and may be unable to return to sleep for a short period of time.[2] Recurrent nightmares may require medical help, as they can interfere with sleeping patterns and cause insomnia. Nightmares can have physical causes such as sleeping in an uncomfortable position or having a fever, or psychological causes such as stress or anxiety. Eating before going to sleep, which triggers an increase in the body's metabolism and brain activity, can be a potential stimulus for nightmares.[3] The prevalence of nightmares in children (5–12 years old) is between 20 and 30%, and for adults is between 8 and 30%.[4] In common language, the meaning of nightmare has extended as a metaphor to many bad things, such as a bad situation or a scary monster or person.