giddy

Synonyms: bemused brainless bubbleheaded capricious careless changeable changeful ditzy dizzy empty-headed erratic fickle flighty flustered frivolous gaga heedless inconstant irresolute irresponsible lightheaded punchy reckless reeling scatterbrained skittish slaphappy swimming thoughtless unbalanced unsettled unstable unsteady vacillating volatile whimsical whirling wild woozy

Antonyms: calm careful level-headed sensible serious