填空题

Nightmare disorder, which is also called dream disorder, is (36) by the occurrence of repeated dreams during which the sleeper feels (37) and frightened. Nightmares are dreams that cause intense fear. During the dream, the sleeper usually (38) or experiences a threat to their life or safety. Nightmares are also reported that do not involve (39) danger. As the dream progresses, the threat to the person usually increases, as does their sense of fear. Waking usually occurs just as that threat or danger reaches its (40) . The person wakes from the nightmare with a (41) sense of fear. Waking is complete, and usually (42) by increased heart rate, sweating, and other symptoms of (43) or fear. Once fully awake, (44) . Because clarity is achieved immediately upon waking, returning to sleep after a nightmare is often difficult. (45) . In addition, people may have problems falling asleep if they are experiencing tension caused by the fear of having nightmares. As a result, these people may have the signs and symptoms associated with mild sleep deprivation. The causes of nightmares are not known for certain. (46) About half of these people are thought to suffer from psychiatric disorders that cause the nightmares.