intuitive
reflexively
unplanned
unthoughted
involuntarily
on the hop
insensibly
spur-of-the-moment
spontaneously
automatism
unconscious
extemporaneously
abrupt
unspontaneously
unceremoniously
on impulse
off the top of one's head
nonspontaneous
autoactive
unstudiedly
impulse buy
ultroneously
blurt out
instantaneously
unceremonially
rock up
unprophetically
unperceivingly
senseless
automaticism
nonmomentary
unhesitantly
semispontaneous
impulse purchase
carelessly
unheededly
unblinkingly
insensate
unheedingly
instinctive
intentionless
out of the blue
autonomic
like a shot
nonconsciously
unanticipatedly
under the radar
unimaginatively
unmomentous
thoughtlessly