During the COVID-19 pandemic, many workers have been forced to work from home. In this situation, the boundaries between work and private life have become particularly blurred, and recovering from work was even more difficult than in traditional times, with negative consequences for workers' health. Among the psychological experiences that might underlie the recovery process, mastery played a crucial role as people sought new stimuli and challenging situations. However, there are few articles that have explored the role of this specific recovery experience, its antecedents, and the health consequences under conditions of work from home. Therefore, in this multiwave study, we aimed to investigate the role of mastery as a mediator between supervisor support and insomnia problems. The study was conducted during the COVID-19 pandemic in Italy and had a three-wave design. A convenience sample of 130 employees (67% women) completed an online questionnaire. Hypotheses were tested using a three-wave autoregressive cross-lagged panel model. According to the results, supervisor support at Time 1 was positively related to mastery at Time 2, which in turn showed a negative association with insomnia at Time 3. The results demonstrated that mastery experiences have played a crucial role during COVID-19 mandatory work from home, which points to some potential implications for workers' health in the adoption of teleworking beyond the emergency situation.