"Sudden reversal" refers to a sudden and unexpected change in direction, opinion, or situation. It means going from one extreme to another very quickly. Full definition
Updated, 6:20 p.m. ALBANY — Republicans apparently seized control of the New York State Senate on Monday, in a stunning and sudden reversal of fortunes for the Democratic Party, which controlled the chamber for barely five months. (cityroom.blogs.nytimes.com)
If each of our holdings turned out to involve similar bets [inflation hedges, interest rate sensitive, single market or asset type etc], we would be exposed to dramatic and sudden reversals in our entire portfolio were investor perceptions of the macro environment to change. (mastersinvest.com)
Sometimes the film seems as full of ups and downs and sudden reversals as any match on center court. (awfj.org)