Hypersomnia is conventionally defined as an inability
to consistently attain and sustain wakefulness
and alertness necessary to meet the demands
and accomplish the tasks of daily living. This definition,
however, poses major challenges to a clinician
who attempts to establish its presence and grade
its severity. Needless to say, it is essential to
distinguish among hypersomnia in which alertness
mechanisms fail, leading to potentially dangerous
sleep attacks; weak alerting systems in which a
sleepy person has to put extra effort to stay awake;
and overactive sleep-promoting processes.