Background The health crisis caused by COVID-19 has led many countries to opt for social quarantine of the population. During this quarantine, communication systems have been characterized by disintermediation, the acceleration of digitization and an infodemic (excess and saturation of information). The following debate arises: Do the levels related to the psychotic phenotype and pseudoscientific beliefs related to the interpretation of information vary before and after social quarantine? Objectives This research aims to examine the psychological effects of social quarantine on the psychotic phenotype and pseudoscientific beliefs-experiences of the general nonclinical population. The following hypothesis was posed: social quarantine alters the levels of magical thinking, pseudoscientific beliefs and anomalous perceptions due to quarantine. Methods A pre- and posttest analysis design was applied based on the difference in means, and complementary Bayesian estimation was performed. A total of 174 Spanish subjects responded to different questionnaires that evaluated psychopathological risks based on psychotic phenotypes, pseudoscientific beliefs and experiences before and after quarantine. Results Significant differences were obtained for the variables positive psychotic symptoms, depressive symptoms, and certain perceptual alterations (e.g., cenesthetic perceptions), and a significant increase in pseudoscientific beliefs was also observed. The perceptual disturbances that increased the most after quarantine were those related to derealization and depersonalization. However, paranoid perceptions showed the highest increase, doubling the initial standard deviation. These high increases could be related to the delimitation of physical space during social quarantine and distrust towards information communicated by the government to the population. Is it possible that social alarmism generated by the excess of information and pseudoscientific information has increased paranoid perceptual alterations? Conclusions Measures taken after quarantine indicate that perceptual disturbances, subclinical psychotic symptoms and beliefs in the pseudoscience have increased. We discuss which elements of quarantine coincide with the social marginality theory and its clinical repercussions.