A nightmare is a dream that causes strong emotional responses from the sleeper, typically fear/horror. The dream may contain situation(s) of danger, discomfort, or psychological or physical distress. Sufferers are usually woken in a state of distress, and might be unable to go back to sleep for a prolonged period.
Nightmares can have physical causes such as sleeping in an uncomfortable or awkward position, or having a fever; and psychological causes, such as stress or anxiety. Eating before bed, which triggers an increase in the body’s metabolism and brain activity, is a potential stimulus for nightmares.
Occasional nightmares are commonplace, but recurrent nightmares can interfere with sleeping patterns and cause insomnia, and may require medical help. A recently proposed treatment consists of imagery rehearsal. This approach appears to reduce the effects of nightmares and other symptoms in acute stress disorder and post-traumatic stress disorder.