light-headedness

noun

light-head·​ed·​ness ˈlīt-ˈhed-əd-nəs 

: the condition of being dizzy or on the verge of fainting

dizziness or light-headedness, particularly when one arises to a standing position, is a predictable consequence of any medication tending to lower blood pressure

—Harvard Medical School Health Letter

light-headed adjective