Anorexia nervosa (AN) is characterized by a strong fear of weight gain and body image disorders and is classified as a mental illness that can cause direct damage to one's mental health and body. Many individuals with AN tend to commit suicide. Additionally, the disease can lead to chronic undernutrition and low body weight, adversely affecting each body system, exacerbating systemic medical complications, especially acute life-threatening complications. Therefore, AN has the highest mortality and disability rates among all mental diseases. There is a basic clinical need to identify and address the acute and critical complications of this disease as soon as possible. However, the current literature has a poor description of the acute and critical complications of AN and lacks a systematic review. We report a case of a patient with AN and severe hypokalemia, significant Q-T interval prolongation, stomach dilation, and intestinal obstruction who recovered after conservative treatment. The defecation method we used, to our knowledge, has not been previously reported in the literature. We also briefly review the various acute and life-threatening complications of AN.