Introduction: This study focused on autonomic nervous system activity during sleep and after arousal and mood changes, and examined the association between mood and emotional changes and autonomic nervous system activity during sleep and after arousal in healthy young individuals through spectral analysis of variations in R-R intervals on electrocardiography as autonomic nervous system activity assessment. Materials and Methods: The subjects involved 20 females students (21.6 ± 0.8) belonging to a medical university located in Japan. At noon on the first and second days, assessment was conducted using the Profile of Mood States (POMS). In addition, from the night of the first day to noon of the second day, measurement was performed with the device ActiHR4 (CamNtech, UK) attached to the subjects. Results and Conclusion: It was confirmed associations of tension and confusion with autonomic nervous system activity during sleep. Also, mood changes showed an association with sympathetic and parasympathetic nervous system activities during sleep, suggesting the possibility of these activities influencing moods.