We report the case of a 32-year-old woman with a history of increased sleep need and difficulty waking up; the diagnosis of idiopathic hypersomnia was hypothesized. During ambulatory polysomnography (PSG), the patient presented an episode characterized by loss of consciousness and jerking of the four limbs. A video-PSG monitoring was performed and the patient showed unresponsiveness and drowsiness at 7 a.m. During the episode, EEG showed theta-delta diffuse activity, and blood glucose level was 32 mg dl(-1). The diagnosis of insulinoma was then assumed; CT scan showed a hypodense mass into the pancreatic tail, and a partial pancreasectomy was performed. The described symptoms disappeared, and 5 years later the findings of a complete clinical and neurophysiological examination were negative. The clinical picture of insulinoma presenting with paroxysmal disorders has been previously described; however, whereas hypersomnia is uncommon, in the current case it represents the main symptom. Clinicians should keep in mind that neuroglycopenia should be considered in the differential diagnosis of patients with hypersomnia, particularly if the clinical scenario does not conform to standard criteria.