'Suddenly', 'Apruptly', and all of their fun synonyms don't exist. They aren't words you're allowed to use. Don't use them. Make the sentence itself abrupt. Active tense. Things happen. To say that things suddenly happen only slows down the sentence and ultimately slows down the action. Use as few words as possible to show the tenseness, the nail-biting sequences.
Don't tell us that it's sudden. Show it.
(Currently revising Chapter 26 - The First Manifestation and it's lovely action scene. It's rather a SUDDEN action scene, as I oft repeated before this revision -.-)