WordNet sense 1 (having or causing a whirling sensation; liable to falling):

dizzy, vertiginous, woozy

WordNet sense 2 (affected by an impairment of normal physical or mental function):

ill, sick

WordNet sense 3 (lacking seriousness; given to frivolity):

empty-headed, lightheaded, silly, airheaded, featherbrained, light-headed

WordNet sense 4 (not serious in content or attitude or behavior):

frivolous