Imagination, fantasies, dreams, and hallucinations are contiguous mental processes that reflect various forms of image processing at the internal level. The ability to maintain boundaries between them, reflecting as they do either external or profoundly internal, subjective reality (reality testing), is considered to be one of the most widely accepted criteria of mental health. Nevertheless, traditionally these processes have been investigated independently by different authors adopting different approaches, and there is a discernible lack of studies dedicated to the comparative analysis of these phenomena, both in their theoretical and empirical aspects. At the same time, such data could be used to develop diagnostic methods of investigating mental processes in normal conditions as well as in cases of mental disorders. The aim of this study is to investigate people's common ideas about imagination, fantasies, dreams and hallucinations, as well as the subjective experience of them in comparison with each other. The study's group of participants consisted of 45 nominally mentally healthy people (32 women and 13 men) aged between 17 and 29 years old. The following methods were used during the study: a semistructured interview aimed at studying the respondents' ideas about imagination, fantasy, dreams and hallucinations, and visual drawings of the forms, which these processes took. According to the results of the study, in the case of 15% of the respondents, their ideas about imagination, fantasies, dreams and hallucinations differed from their scientific definitions. The drawings of the images of imagination, fantasies, dreams and hallucinations varied in terms of emotional experience. The more the mental process is voluntary and subjectively controlled, the more these images are associated with positive emotions. In particular, images of imagination are mainly associated with a positive emotional charge, images of fantasy more often evoke positive emotions, but also ambivalent experiences, and drawings of the images of dreams and hallucinations are most often associated with negative emotions.