An overnight sleep study is necessary to diagnosis the cause of your excessive daytime sleepines. It could be caused by obstructive sleep apnea, idiopathic hypersomnia or Upper Airway Resistance Syndrome (UARS).
08 September 2014
Events: September 8-14, 2014 is Idiopathic Hypersomnia Awareness Week
From the Hypersomnia Foundation website:
"Hypersomnia is a debilitating neurological disorder where patients lose their cognitive ability, sleep excessively, yet still crave sleep above all else. ...This means they often struggle to work, operate a vehicle or live independently. In fact, often just waking up is an ordeal in and of itself with even sonic boom alarms, the help of family and powerful stimulants not being enough. While the onset of symptoms is generally in early adulthood it routinely takes up to a decade for new patients to be formally diagnosed…"

If you feel excessively sleepy, day in and day out, and you want your energy and your hours back (!), please consult your physician about potential causes.