Cognitive accounts of insomnia generally assume that excessive mental activity at bedtime constitutes a central impediment to the process of falling asleep, yet the affective aspects of this mental hyperactivity still remain largely unexplored. The present study explored whether failures in regret anticipation might lead to a rise of regret-related counterfactual thoughts and emotions at bedtime, thereby hindering or interrupting sleep. A sample of 105 undergraduate students completed the newly developed Regret Anticipation Failures Scale (RAFS), the Bedtime Counterfactual Processing Questionnaire (BCPQ), and the Insomnia Severity Index (ISI). Analyses revealed that both regret anticipation failures and bedtime counterfactual processing were related to insomnia severity and that the effect of regret anticipation failures on insomnia was mediated by the frequency of regret-related thoughts and emotions at bedtime. These findings reveal for the first time that failures in antecedent-focused emotion regulation may contribute to sleeping difficulties.