A consistent body of evidence suggests that excessive cognitive activity at bedtime is a key factor in insomnia. It is generally assumed that sleep-interfering cognitions are affect laden, but still little is known about the precise nature of the affective processes that are involved. The present study sought to explore the role of counterfactual thinking and counterfactual emotions (regret, shame, and guilt) in insomnia as a function of impulsivity. It was hypothesized that when retiring for the night, individuals scoring high on urgency review their rash daytime behavior and are therefore likely to engage in counterfactual thinking and to experience associated feelings of regret, shame, and guilt. A sample of 101 undergraduate students completed three questionnaires: the UPPS Impulsive Behavior Scale, the Bedtime Counterfactual Processing Questionnaire, and the Insomnia Severity Index. Results indicated that both urgency and counterfactual processing were related to insomnia severity and that the effect of urgency on insomnia was mediated by counterfactual processing. These findings reveal for the first time that impulsivity relates to counterfactual cognitive-affective processing and that this type of processing contributes to sleep disturbances.