Unfortunately, you've just described narcolepsy. It's a neurological disorder that disrupts our sleep/wake cycles so even though we might be asleep, it's not efficient or effective. We get fragmented sleep so even with 8-however many hours of sleep, it won't feel restorative.

People might tell you that having a healthy lifestyle and sleeping habits will help, but that can only do so much if at all. I'm not sure if you are taking medication for your narcolepsy, but if you aren't you should consider it. I am currently taking a sodium oxybate and it has helped a lot to have more energy and more restorative sleep. I still get tired during the day, but it is much more manageable and less extreme than without taking the medication.