WordNet sense 1 (weak and likely to lose consciousness):

faint, light, light-headed, swooning

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

ill, sick

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

dizzy, empty-headed, giddy, silly, airheaded, featherbrained

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

frivolous