What causes excessive sleepiness?

Hypersomnolence.: Other than this answer? Hypersomnolence must be differentiated from fatigue. Excessive sleepiness can result from a decreased wake drive (the scn is off-i.e. You are awake when you should be sleeping such as shift workers) or an increased sleep debt is owed (lack of sleep or unrestorative sleep), or a combination of the two. Causes can include narcolepsy, osa, swd, metabolic or medication effects.

Sleep Apnea: If you have symptoms such as insomnia snoring hypersomnia excessive daytime sleepiness obesity asian race cognitive deficits mood disorders htn etc increase the chance of sleep apnea rule out other causes, could be medical, genetic long sleeper etc.