Hypersomnia is the need for a higher than average amount of sleep. (Hyper = more, somnia = sleep) It is not necessarily related to any other sleep abnormality. It is not caused by a lack of sleep, nor by sleep of inferior quality. These will lead to the same symptoms as hypersomnia: tiredness and an inability to stay awake, but hypersomnia is a different condition. With other disorders, insomnia for example, if that were cured, the person would then only need a normal amount of sleep (about 8 hours per night). Hypersomnia is where, even if your sleep is restful and untroubled, you need more than 10 hours sleep a night to be fully rested. As far as I know, there is no treatment for hypersomnia except, well, sleeping more.