impetuous

Synonyms: abrupt ardent eager fervid fierce furious going off deep end hasty headlong hurried impassioned impulsive passionate precipitant precipitate precipitous rash restive rushing spontaneous spur-of-the-moment subitaneous sudden swift unbridled unexpected unplanned unpremeditated unreflecting unrestrained unthinking vehement violent

Antonyms: calm cautious circumspect considerate reflective sensible thoughtful wise