nesvestica

1. faintness; fainting spell
   Uhvatila me je nesvestica u punom autobusu. — I felt faint on the crowded bus.
   Od vrućine je dobila nesvesticu i morala je da sedne. — The heat made her feel faint and she had to sit down.

Usually the feeling of being about to faint; full loss of consciousness is "nesvest" (pasti u nesvest).