Mass psychogenic illness (MPI), sometimes called mass hysteria, refers to the rapid spread of illness signs and symptoms within a cohesive group without an identifiable infectious agent or environmental toxin. Documented episodes have occurred across centuries and societies; one recorded outbreak noted on June 11 (exact year not preserved in some sources) fits this pattern of sudden, clustered somatic complaints that proved transient and noninfectious. Typical features of MPI seen in such outbreaks include a predominance of subjective symptoms—headache, dizziness, nausea, fainting, shortness of breath, and numbness—often with rapid escalation among exposed individuals. A key epidemiological clue is the absence of laboratory or clinical evidence of a common pathogen or toxin, paired with a clear social connection among affected persons (for example, a school, workplace or community gathering). Media attention, anxiety about perceived threats, and preexisting social tensions frequently amplify and prolong episodes. Investigations into historical MPI events emphasize careful clinical assessment, environmental testing, and evaluation of social dynamics. Medical teams rule out infections, chemical exposures, and other organic causes through history-taking, physical examination, and appropriate laboratory or environmental analyses. When these yield no causative agent, clinicians and public-health officials often consider psychogenic mechanisms, particularly when symptoms are stereotyped, short-lived, and disproportionately affect socially linked individuals. Management of MPI focuses on clear, calm communication, reassurance, and addressing contributing stressors. Removing affected individuals from the triggering environment, providing symptomatic care, and restoring normal routines often halt further spread. Public-health messaging that transparently explains findings—while avoiding alarmist language—reduces anxiety and counters rumor-driven transmission. Historians and clinicians studying past outbreaks caution against pejorative labeling. Describing an event as psychogenic does not imply that symptoms are feigned; they are real and can cause significant distress and disability. Rather, the term highlights the role of psychological, social, and contextual factors in symptom genesis and propagation. Because the date of June 11 is cited in some records without an accompanying year, attribution of this specific entry to a single well-documented, peer-reviewed case is uncertain. Where archival records or contemporary reports are incomplete, historians note the date while acknowledging gaps in provenance. For readers seeking primary-source documentation, contemporaneous medical reports, public-health bulletins, and reputable historical reviews are appropriate next steps; these sources can confirm investigations, laboratory results, and public-health responses for particular outbreaks. MPI remains an important concept in public health because it illustrates how fear, social contagion, and contextual stressors can produce widespread, noninfectious illness. Recognizing the phenomenon enables health professionals to conduct appropriate investigations, avoid unnecessary interventions, and implement communication strategies that restore public confidence and reduce harm.