drowsy (adj.)youdaoicibaDictYouDict
1520s, probably ultimately from Old English drusan, drusian "sink," also "become languid, slow, or inactive" (related to dreosan "to fall"), from Proto-Germanic *drus- (see dreary). But there is no record of it in Middle English. Related: Drowsily; drowsiness.
nystagmus (n.)youdaoicibaDictYouDict
medical Latin, from Greek nystagmos "nodding, drowsiness," from nystazein "to nod, be sleepy," from PIE *sneud(h)- "to be sleepy."
Somnus (n.)youdaoicibaDictYouDict
"sleep personified; the god of sleep in Roman mythology," equivalent of Greek Hypnos, son of Night and brother of Death, 1590s, from Latin somnus "sleep, drowsiness," from PIE *swep-no-, from root *swep- (1) "to sleep" (cognates: Sanskrit svapnah, Avestan kvafna-, Greek hypnos, Lithuanian sapnas, Old Church Slavonic sunu, Old Irish suan, Welsh hun "sleep," Latin sopor "a deep sleep," Old English swefn, Old Norse svefn "a dream").
oscitancyyoudaoicibaDictYouDict
"Drowsiness as evidenced by yawning; dullness; indolence, negligence, inattention", Early 17th cent. From oscitant: see -ancy). Compare post-classical Latin oscitantia.