The COVID-19 vaccination has been the subject of unprecedented misinformation, false news, and public concerns. This study presents a unique analysis comprising persons who were not vaccinated and became ill. It investigates reasons for not vaccinating and evaluates how the personal experience of COVID-19 affected further attitudes and decisions related to health. The study included 730 consecutive unvaccinated patients hospitalized in 12 centers in Poland during the autumn 2021 pandemic wave. The most frequent reason behind the refusal to receive the vaccine was concern over the adverse effects, disbelief that the vaccine was sufficiently tested, and one’s conviction that COVID-19 will not affect a patient. Online information, friends, spouse, children/grandchildren, and other family members were most often the source of discouragement from vaccination. Most individuals regretted their decision not to receive a vaccine (66.0%), declared to promote COVID-19 vaccination after discharge (64.0%), and to receive a COVID-19 vaccine in the time recommended for convalescents (69.5%). Individuals expressing no regrets of vaccine refusal more frequently revealed conspiracy beliefs. The study shows that personal experience with severe COVID-19 can influence the perception of vaccination, but approximately one-third of unvaccinated hospitalized patients still appear to express vaccine hesitancy.