Henry Fuseli - The Nightmare (1782)
A nightmare is a dream that can cause a strong negative emotional response from the sleeper, typically fear and/or 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. [...]
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.[2] This approach appears to reduce the effects of nightmares and other symptoms in acute stress disorder and post-traumatic stress disorder.[3]
Source : Our usual one, Wikipedia.
