impulsive

Synonyms: abrupt ad-lib automatic careless devilmay-care emotional extemporaneous flaky gone off deep end hasty headlong hot-and-cold impetuous instinctive intuitive involuntary jumping the gun mad offhand passionate precipitate quick rash spontaneous sudden swift unconsidered unexpected unmeditated unpredictable unpremeditated unprompted up-and-down violent winging it

Antonyms: cautious considering heedful premeditative thoughtful wise