The relationship of dream frequency and dream contents during night sleep and dream memory to sleep habits, circadian typologies and mental symptoms and also to the 24-h society was studied in Japanese students. A morningness-eveningness questionnaire by Torsvall and Åkerstedt and another questionnaire to elicit the relationship between sleep habits, mental symptoms (depression, irritability and anger), dreaming (frequency, contents, duration and tendency to remember dreams) and the 24 h a day commercialization of Japanese society (using convenience stores open for 24 h a day and mobile phones, and watching midnight TV) were administered to 461 students attending university or medical training schools (senior students, nurses and physical and occupational therapists aged 18-25) in the Kochi Prefecture, 33°N. Students who dreamt frequently had more difficulty in waking up and felt irritation and depression more frequently than those who did not. Students who had negative dreams (in which they were frightened, sad, lonely and angry) felt depressed or were easily and unreasonably angered more frequently than those who had positive (happy) dreams. The frequent use of convenience stores and personal computers was positively correlated to frequent dreaming. Students who watched midnight TV suffered sleep paralysis more frequently than those who did not. Frequent negative dreams and the frequent occurrence of sleep paralysis, both of which might be triggered by the 24 h a day commercialization of Japanese society may be linked to the worse mental health of older Japanese students.Key words: 24 h a day society, dreaming by Japanese students aged 18-25 years, mental health, morningness-eveningness, sleep habits.Dreams and sleep habits of 18-25-year-old students

Questionnaires on morningness-eveningness by Torsvall and Åkerstedt, sleep habits, psychiatric aspects and dreaming were administered to 870 students aged 12-15 years attending one of two junior high schools located in urban area in Kochi city (33°N) and suburban and neighboring area. Students who had negative dreams that were frightening, sad and so on tended to have later bedtimes and a shorter sleep duration and more frequently felt depressed or were unreasonably easily angered than those who had happy dreaming. A later bedtime may be related to a higher frequency of negative dreaming, which seems to trigger mental symptoms such as a depressed mood and irritation in Japanese adolescents.