[填空题]Nightmare disorder, which is also called dream disorder, is{{U}} (36) {{/U}}by the occurrence of repeated dreams during which the sleeper feels{{U}} (37) {{/U}}and frightened. Nightmares are dreams that cause intense fear. During the dream, the sleeper usually{{U}} (38) {{/U}}or experiences a threat to their life or safety. Nightmares are also reported that do not involve{{U}} (39) {{/U}}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{{U}} (40) {{/U}}. The person wakes from the nightmare with a{{U}} (41) {{/U}}sense of fear. Waking is complete, and usually{{U}} (42) {{/U}} by increased heart rate, sweating, and other symptoms of{{U}} (43) {{/U}}or fear. Once fully awake,{{U}} (44) {{/U}}. Because clarity is achieved immediately upon waking, returning to sleep after a nightmare is often difficult. {{U}} (45) {{/U}}. In addition, people