Anti-IgLON5 antibody-related encephalopathy is a recently discovered and rare autoimmune disease, and its diagnosis and treatment are more challenging than for other autoimmune encephalopathic diseases. Sleep disorder is the most prominent symptom of the disease. It can also present with gait instability, dysarthria, dysphagia, dementia, ataxia, autonomic nervous system dysfunction, chorea, vertical gaze paralysis, and other symptoms. Immunotherapy remains the primary treatment for this disease; however, there is no definitive conclusion regarding the effect of immunotherapy. The clinical symptoms of the reported cases of anti-IgLON5 antibody-related encephalopathy were generally severe. However, the symptoms in our patient were mild and relieved without immunotherapy, unlike the previously reported cases.