surprising
abrupt
alarming
amazing
astonishing
astounding
awesome
awing
breathtaking
chilling
confounding
daunting
deterrent
deterring
disconcerting
discouraging
disheartening
dismaying
disquieting
disturbing
electrifying
eye-opening
fear-inspiring
fearful
fearsome
frightening
frightful
hasty
headlong
impetuous
impulsive
jarring
jolting
mind-boggling
nerve-shattering
overawing
overwhelming
precipitant
precipitate
precipitous
quick
scaring
scary
shocking
spectacular
speedy
staggering
stunning
sudden
swift