vertiginous \vur-TIJ-uh-nuhs\, adjective
1. Affected with vertigo; giddy; dizzy.
2. Causing or tending to cause dizziness.
3. Turning round; whirling; revolving.
4. Inclined to change quickly or frequently; inconstant.
The look in his eyes made her feel particularly vertiginous, and the feeling almost made her lose her balance.
Vertiginous derives from Latin vertigo, "a turning round, a whirling round; giddiness," from vertere, "to turn." Related words include reverse, "to turn back (re-) or around"; subvert, "to undermine" (from sub-, "under" + vertere -- at root "to turn from under, to overturn"); and versus, "against" (from versus, "turned towards," hence "facing, opposed," from the past participle of vertere).