**5. Conclusions**

Perceived stress, life satisfaction, and coping styles significantly changed from the first to the second wave of the COVID-19 pandemic. University students considered changes in lifestyle and environment related to lockdown and adjusted their best coping strategies to these stressful events. As such, stress, and emotion-oriented and avoidance-oriented coping styles increased from W1 to W2, while life satisfaction and task-oriented coping decreased. These variables explained almost 70% of the variance in life satisfaction as stress and life satisfaction during W1, stress during W1 and W2, and emotion-oriented and taskoriented coping during W2. In the cross-sectional study, coping styles played a mediating role in the relationship between stress and life satisfaction at W1 and W2. However, in the longitudinal design, coping during W1 was not a useful predictor of life satisfaction or stress during W2. We found a reciprocal interrelation between stress and life satisfaction. Therefore, we found strong evidence aligned with the theory of the transactional model of stress. The findings provide new knowledge on our current understanding of stress and coping mechanisms concerning well-being. People try various coping strategies and choose the most effective at the moment and change them in response to the unstable environment. A vast repertoire of coping strategies, and flexibility in their selection, may be the best methods to effectively cope with stressful lockdowns during the COVID-19 pandemic and protect individuals against decreased well-being.

**Author Contributions:** Conceptualization, A.M.R., C.K. and D.O.; methodology, A.M.R. and D.O.; software, A.M.R.; validation, A.M.R., C.K. and D.O.; formal analysis, A.M.R.; investigation, C.K.; resources, A.M.R.; data curation, A.M.R.; writing—original draft preparation, A.M.R.; writing—review and editing, A.M.R., C.K., D.O.; visualization, A.M.R.; supervision, D.O.; project administration, C.K.; funding acquisition, C.K. and D.O. All authors have read and agreed to the published version of the manuscript.

**Funding:** The study was not financially supported by any grant or foundation. The APC was funded by the Opole University of Technology and University of Technology in Katowice.

**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 University of Opole (protocol code 1/2020, date of approval 22 April 2020).

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

**Data Availability Statement:** The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

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