nystagmus (n.)

"involuntary motion of the eyes," 1790, medical Latin, from Greek nystagmos "nodding, drowsiness," from nystazein "to nod, slumber, be sleepy," from PIE *sneud(h)- "to be sleepy." Beekes compares Baltic words such as Lithuanian snūsti "to slumber away." Related: Nystagmatic.