Currently, undiagnosed insulinomas remain a difficult clinical dilemma because its symptoms in most cases can easily be misdiagnosed as other diseases. In this article, we present the case of a 14-year-old girl who presented to our hospital with recurrent episodes of excessive daytime sleepiness and abnormal behavior during sleep that had been going on for 3 months. Insulinoma is a rare neuroendocrine tumor that causes excessive release of insulin, resulting in episodes of hypoglycemia. It usually manifests as autonomic sympathetic symptoms. These symptoms resolved rapidly with the administration of glucose. After successful removal of the tumor, daytime sleepiness and abnormal nighttime behavior of the patient did not reappear.