A nightmare, also called a bad dream, 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. Recurrent nightmares may require medical help, as they can interfere with sleeping patterns and cause insomnia.