U.S. stocks extended a punishing selloff, dragged to their worst week since the financial crisis by mounting investor unease about the economic fallout from the coronavirus epidemic.

Friday’s session was marked by wild swings that sent the Dow Jones Industrial Average down more than 1,000 points before it rallied around 640 points in the final minutes of trading. The Nasdaq Composite fell as much as 3.5% before bouncing higher to narrowly close in positive territory—the first time the index has fallen by that much and notched a gain for the day since November 2008, according to Dow Jones Market Data.

Some of the most dramatic moves happened after the Federal Reserve’s unexpected attempt to calm markets at the very tail end of a volatile week. Late in the afternoon, Fed Chairman Jerome Powell signaled that the central bank was prepared to cut interest rates to protect the economy from the widening global slowdown. Stocks initially pared losses after the announcement, dropped again, then climbed rapidly into the close.

Still, the weekly losses were broad. The Dow Jones Industrial Average fell 12.4% this week, a drop of more than 3,500 points, capping off its worst month since 2009. All 11 of the S&P 500’s sectors have fallen into negative territory for the year. About 95% of stocks in the broad index are now down more than 10% from their highs, according to Dow Jones Market Data.

Traders and investors described a feeling of mounting apprehension throughout the week, as major U.S. indexes logged a series of slides unseen in years and bond yields fell to historic lows.