"excessive sleeping or morbid sleepiness," 1863; see hyper- + ending from insomnia. Related: Hypersomniac.
Entries linking to hypersomnia
hyper-
word-forming element meaning "over, above, beyond," and often implying "exceedingly, to excess," from Greek hyper (prep. and adv.) "over, beyond, overmuch, above measure," from PIE root *uper "over."
insomnia n.
"chronic inability to sleep," 1620s, insomnie, from Latin insomnia "want of sleep, sleeplessness," from insomnis "sleepless," from in- "not" (see in- (1)) + somnus "sleep" (from PIE root *swep- "to sleep"). The re-Latinized form is from 1758.