You are most likely suffering from hypersomnia. It may present as excessive daytime sleepiness or nocturnal sleep of long duration (as much as 12 h or more) or sleep drunkenness.
Patients do not get abnormal amounts of night sleep rather they have problems waking up in the morning and staying awake during the day.
Hypersomnia is sometimes misdiagnosed as narcolepsy where a person experiences a sudden onset of sleepiness. The causes can be genetic, brain damage or medical disorders such as clinical depression, uremia and fibromyalgia. Sometimes hypersomnia may be other sleep disorders such as narcolepsy, sleep apnea, and restless leg syndrome.
You should consult a psychologist for a complete medical and psychological workup.
Do keep us posted about your progress.
I also have the same problem..cant here the 4 alarms in the mornig, nobody is able to wake me and i sleep 11-18 hours if left to wake on my own..i have been dx with fibro/cfs but i have had this seeping problem since a child..the fibro members mostly are opposit in sleep problems so am wondering why am the other way around..
let us know how you get on and if you can find any answers for yourself
best of luck