This case report describes the diagnostic and therapeutic course of a 42-year-old male patient who initially presented with nonspecific gastrointestinal complaints. Despite an extensive somatic diagnostic workup—including laboratory testing, ultrasound, endoscopic examinations, and CT imaging—no organic cause of the symptoms was identified. A presumed diagnosis of SIBO led to temporary improvement following dietary measures and antibiotic treatment. However, the patient subsequently experienced an unexpected progression of psychiatric symptoms, including sleep disturbances, affective lability, and suicidal ideation. After an acute psychiatric evaluation, a diagnosis of severe depressive disorder was established, and the patient was admitted to a psychiatric clinic. This case highlights the complex interplay between somatic and psychological symptoms and underscores the importance of early recognition of psychiatric comorbidity in patients with long-standing unexplained physical complaints.A detailed clinical evaluation was conducted, including comprehensive somatic diagnostics (laboratory tests, abdominal ultrasound, endoscopy, and CT imaging) followed by targeted gastroenterological treatment for suspected SIBO. As the symptom pattern evolved, psychiatric assessment was performed to clarify the emerging affective and cognitive disturbances.This case uniquely demonstrates how initially isolated gastrointestinal symptoms can mask an underlying depressive disorder that rapidly progresses to a severe episode with psychotic features. It highlights an uncommon but clinically significant transition from somatic presentations to acute psychiatric decompensation.The case underscores the importance of early psychiatric consideration in patients with persistent, unexplained somatic complaints. It suggests that integrating routine psychosocial screening into somatic diagnostic pathways could facilitate earlier detection of somatized depressive disorders and reduce the risk of progression to severe forms, including suicidal behavior.The observed clinical trajectory illustrates the complexity of mind–body interactions and the potential for somatic symptoms to represent prodromal phases of major psychiatric illness. The case highlights the necessity of interdisciplinary communication between primary care, gastroenterology, internal medicine, and psychiatry to ensure timely intervention and comprehensive patient care.This case reinforces the value of a holistic, bio-psycho-social approach in everyday clinical practice. Early recognition of psychiatric comorbidity in patients with chronic, unexplained somatic symptoms is essential for preventing escalation into severe depressive episodes and for improving overall diagnostic and therapeutic outcomes.