**5. Conclusions**

The present longitudinal work showed that the detrimental effect of the first Italian COVID-19 lockdown on sleep was fully mediated by mindfulness and distress and that these effects were dependent on the acceptance component working through anxiety, thus confirming our hypotheses based on previously published cross-sectional results [14,20]. By significantly advancing our knowledge of the mechanisms linking sleep to mindfulness and distress, this work not only adds evidence to the mounting literature recommending the use of mindfulness-based interventions to treat insomnia and sleep disturbances, but it also suggests the possibility to develop novel mindfulness-based interventions that focus particularly on acceptance for preventing sleep problems in stressful situations.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/ijerph182413149/s1, Table S1: MirolliEtAl\_IJERPH\_SupplementaryMaterialS1\_Data.csv.

**Author Contributions:** Conceptualization, M.M. (Marco Mirolli), L.S., M.M. (Monica Martoni) and M.F.; Data curation, M.M. (Marco Mirolli), L.S. and M.F.; Formal analysis, M.M. (Marco Mirolli), L.S. and M.F.; Investigation, M.M. (Monica Martoni) and M.F.; Methodology, M.M. (Marco Mirolli), L.S. and M.F.; Project administration, M.M. (Marco Mirolli) and M.F.; Resources, M.F.; Software, L.S.; Supervision, M.M. (Marco Mirolli) and M.F.; Validation, L.S.; Visualization, L.S.; Writing—original draft, M.M. (Marco Mirolli) and M.F.; Writing—review & editing, L.S. and M.M. (Monica Martoni). All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of the Department of Psychology at the University of Campania Luigi Vanvitelli (protocol code Fabbri\_5/2020).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available in Table S1.

**Conflicts of Interest:** The authors declare no conflict of interest.
