impulsive
unplanned
a bit previous
ad lib
ad-lib
advanced
automatic
casual
caught napping
caught off balance
caught short
coincidental
extemporaneous
extemporary
extempore
extemporized
far ahead
forward
gut
half-baked
half-cocked
haphazard
hasty
ill-advised
ill-considered
ill-devised
impromptu
improvised
inadvertent
indeliberate
involuntary
last-minute
makeshift
natural
not firm
off the cuff
offhand
overhasty
oversoon
precipitate
precocious
premature
previous
reflex
reflexive
rough-and-ready
rushed
snap
spontaneous
spur-of-the-moment
surprised
artless
effortless
exhaustless
fortuitous
incidental
motiveless
premeditated
purposeless
reasonless
sublimest
torrential
unconnected
uncontrollable
undesigned
unimpressed
unintentional
unprovoked
unsought
unstudied
untaught
virtuous