The term ‘hypersomnia’ describes a group of symptoms that includes severe daytime sleepiness and sleeping long periods of time (more than 10 hours per night). Sometimes, hypersomnia is caused by a problem with the quality of sleep occurring at night, for instance when nighttime sleep is disrupted by frequent breathing pauses. In other cases, however, hypersomnia occurs even when nighttime sleep is of good quality. These cases of hypersomnia are presumed to be a symptom of brain dysfunction, and so are referred to as hypersomnias of central (i.e., brain) origin, or primary hypersomnias. The causes of most of these primary hypersomnias are not known. However, our group has recently identified a problem with the major brain chemical responsible for sedation, known as GABA. In a subset of our hypersomnia patients, there is a naturally-occurring substance that causes the GABA receptor to be hyperactive. In essence, it is as though these patients are chronically medicated with Valium (or Xanax or alcohol, all substances that act through the GABA system), even though they do not take these medications. Current treatment of central hypersomnias is limited. For the fraction of cases with narcolepsy, there are FDA-approved, available treatments. However, for the remainder of patients, there are no treatments approved by the FDA. They are usually treated with medications approved for narcolepsy, but sleep experts agree that these medications are often not effective for this group of patients. Based on our understanding of the GABA abnormality in these patients, we evaluated whether flumazenil (an medication approved by the FDA for the treatment of overdose of GABA medications or the reversal of GABA-based anesthesia) would reverse the GABA abnormality in our patients. In a test tube model of this disease, flumazenil does in fact return the function of the GABA system to normal. The investigators have treated a few patients with flumazenil and most have felt that their hypersomnia symptoms improved with this treatment. To determine whether flumazenil is truly beneficial for primary hypersomnia, this study will compare flumazenil to an inactive pill (the placebo). All subjects will receive both flumazenil and the placebo at different times, and their reaction times and symptoms will be compared on these two treatments to determine if one is superior. Currently, flumazenil can only be given through an injection into a vein (i.e., intravenously). This study will evaluate this intravenous dosing as well as a new form of flumazenil, which is taken as a lozenge to be dissolved under the tongue. If this study shows that flumazenil is more effective than placebo in the treatment of hypersomnia, it will identify a potential new therapy for this difficult-to-treat disorder.