hypersomnia
Medical term for excessive sleepiness or prolonged nighttime sleep. Used in clinical contexts.
Patients with hypersomnia often feel strong sleepiness during the day.
General term for sleep disorders; 過眠症 is a specific type.
idiopathic hypersomnia
Compound of 過 (excessive) + 眠 (sleep) + 症 (condition/syndrome). A straightforward medical term.