Idiopathic hypersomnia is an uncommon sleep disorder that causes you to be excessively sleepy during the day even after a good or prolonged night's sleep. It also often causes difficulty waking up after you've been asleep at night or for a nap.
Long time while taking a nap
Difficulty waking up
Prolonged sleeping at night
Right after sleeping
If you have Idiopathic Hypersomnia, then a visit to a neurologist is recommended.