Precipitous

quick rapid sudden brief hasty rushing hurried unanticipated unexpected impetuous rash reckless abrupt impulsive plunging violent headlong unforeseen initial heedless gone off half-cocked ill-advised without warning frantic indiscreet madcap uncontrolled willful breakneck impatient jump the gun precipitant off the top of head off the hip harum-scarum refractory swift subitaneous