The first thing I would do is see your family doctor. Ask for a thyroid panel, CBC, serum iron and ferritin. It's entirely possible that you've got anemia or some other kind of medical condition that's causing your lethargy. If those all come up normal, consider asking for a referral to a sleep clinic. There are so many people that have sleep apnea and don't know it-- which can cause you to still feel exhausted even after hours of sleep.

And finally, if all of that checks out, consider stress levels and/or depression. For some of us, our bodies respond to chronic stress by shutting down (like the fight, flight, or freeze response-- hypersomnia is a form of "freeze.") There are medications that can boost energy levels if your hypersomnia is caused by depression. Wellbutrin, for those who can tolerate it, is great for boosting energy levels.

Good luck.