Synonyms and related words :
abrupt, electrifying, extraordinary, hasty, headlong, impetuous, improbable, impulsive, more than expected, nerve-shattering, out-of-the-way, past expectation, precipitant, precipitate, precipitous, quick, shocking, speedy, startling, sudden, surprising, swift, unannounced, unanticipated, undivined, unexpected, unforeseeable, unforeseen, unguessed, unheralded, unhoped for, unlooked-for, unpredictable, unprepared for, without warning