When a person sleeps more than they actually need too then your body cannot adjust right so you feel tired after sleeping more often.
It seems that when you sleep more then you would feel more rested but that doesn't usually happen as our brains are wired to only need a certain amount of sleep.
When you sleep more than you need then your sleeping and REM cycle get messed up so your brain doesn't detect that your body has slept more and rested.
The most sleep a person needs is between 7 to 10 hours of sleep and sleeping more than 10 hours may make you more tired.
On the weekends I sleep around 10 hours but if I sleep any longer than that I actually feel more tired.
You could also have other medical conditions that make you want to sleep more and cause you to still be groggy and tired.