Introduction: The aim of this case report was to investigate the relationship between sleep disorders and audio vestibular symptoms.   Case Report: A case of undiagnosed sleep disorder, presenting as a temporary auditory processing difficulty, is presented. The disorder was initially treated as sudden deafness with dizziness. A 23-year-old male patient complained of acute hearing disturbance despite normal results on pure tone audiometry. The patient was initially administered a steroid injection in the hospital. After treatment, his hearing symptoms improved only slightly and he reported balance difficulty with rightward spontaneous nystagmus. Vestibular rehabilitation was performed. We also suspected that his hearing symptom was due to an auditory processing difficulty. Despite steroid treatment and vestibular rehabilitation, neither of his symptoms improved. We subsequently identified the presence of insomnia. He was prescribed zolpidem 5 mg, which slightly improved his symptoms, and referred to a sleep specialist for further examination. Polysomnography was performed, which identified restless leg syndrome and sleep disturbance with delayed sleep phase syndrome. After pharmacological treatment, his sleep disturbance, hearing difficulty, and balance disorder completely resolved.   Conclusion: Sleep disorders may provoke reversible auditory processing difficulties. We should carefully evaluate patients for a potentially undiagnosed sleep disorder, even in patients chiefly complaining of intractable sensory dysfunction such as hearing or balance disturbance.