just like eating, doing anything too much or too little is usually not a great idea. I'm not sure how much is too much though, and it very from one person to the other. on a whole an adult should sleep between 6-8 hours every night, if you feel a need to sleep an hour or two more, I'm sure it's fine.
If it's a lot past 8 hours, then I think you should get checked up, it might be a medical problem, like lack of vitamins, depression, chronic tiredness and so on.
Also, in might be some sort of sleeping disorder, it might be that your quality of sleep is bad, or that you have insomnia or that your dream sleep is not working properly. Also it might be that your biological clock is tuned to want to sleep at certain hours and that if you find what those hours are and sleep in them, you'll be less tired.
I would get a physical check up and if nothing comes up, try getting checked in a sleep clinic.