This study compared the effects of three experimental conditions on sleep: regret (negative emotion condition), pride (positive emotion condition), and description of a typical working day (emotionally neutral condition). A sample of 176 undergraduate students received sealed envelopes to be opened prior to sleep in the evening. The evening envelope contained instructions to describe either ‘‘your most burdensome regret,'' ‘‘the action you are most proud of,'' or, in a neutral and objective manner, a typical day during the working week. The morning envelope contained instructions to rate total wake time, sleep-onset latency, and total sleep time the preceding night. Additional questionnaires on insomnia severity, trait anxiety, and counterfactual processing were completed in a larger data collection session. Analyses revealed that in participants with habitually high levels of regret, focusing on regret prior to sleep significantly delayed sleep onset in comparison with the neutral condition. This effect was independent of preexisting levels of insomnia severity and trait anxiety. In contrast, focusing on pride prior to sleep did not significantly alter sleep, as compared with the neutral condition. These findings suggest that emotional arousal may contribute to sleep disturbance and should be clearly distinguished from cognitive arousal in the etiology of insomnia.