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.