Currently, a very important thread of research on COVID-19 is to determine the dimension of the psychopathological emotional reactions induced by the COVID-19 pandemic. A non-experimental online research project was designed to determine the predictors of the severity of psychopathological symptoms, such as depression and PTSD symptoms, and the nature of the feedback mechanism between them in groups of men, remaining in hospital isolation due to infection and at-home isolation during the COVID-19 epidemic. The presence of symptoms of depression, post-traumatic stress disorder (PTSD) and a sense of threat due to the pandemic were assessed using the following screening tests: IES-R by Weiss and Marmar, PHQ-9 by Spitzer et al., and a self-constructed sliding scale for assessing COVID-19 anxiety. The study was carried out on a group of 57 firefighting cadets, hospitalized in a COVID-19 isolation room (Mage = 23.01), staying in isolation due to SARS-CoV-2 virus infection and a control group of 57 healthy men (Mage = 41.38) staying at home during quarantine and national lockdown. COVID-19 pandemic causes many psychopathological reactions. The predictive models revealed that the predictors of symptoms of PTSD in isolated patients included depression and the experienced sense of COVID-19 threat resulting from the disease, while in the control group the symptoms of depression were the only predictor of PTSD. PTSD experiences are usually associated with depression. It may also be a form of the re-experiencing process or the effect of high affectivity, indirectly confirmed by the participation of hyperarousal in the feedback loop. Our findings highlight the importance of mental health aspects in patients treated during the COVID-19 pandemic. The COVID-19 pandemic requires social distancing, quarantine and isolation, which may cause psychopathological symptoms not only in affected people, but also in the general population. Moreover, the need for greater psychological support can be emphasized for both: the sick and the general population.