Insulinoma is a rare endocrine tumor that frequently causes neurologic symptoms. We report a case of a 17-year-old man with hypersomnia and abnormal behavior lasting for 10 months. He had recurrent attacks of hypersomnia that lasted for up to 36 hours and of unconscious wandering mimicking an ictal or postictal state. Hypoglycemia was documented (30 mg/dL) and insulinoma was found at the most-recent episode. Clinicians should be aware that hypersomnia and unconscious wandering can present in association with hypoglycemia.