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U.S. markets wrapped up one of their messiest-ever weeks Friday, recording their worst finish since the 2008 financial crisis. The Standard & Poor’s 500 tumbled 15 percent from where it began Monday.

The craziness ran right up to Friday’s closing bell, as the S&P and Dow Jones industrial average plunged more than 3 percent minutes after the World Health Organization warned that world health systems were “collapsing” under the strain of the pandemic.

The Dow shed 913.21 points, or 4.6 percent, to close at 19,173.98 — erasing all Trump-era gains. The S&P closed down 4.3 percent while the tech-heavy Nasdaq composite slid nearly 3.8 percent.

Investors remain in the same fog they have inhabited since markets began their swift drop in February after the S&P and Dow had reached all-time highs. All three indexes are now in a bear-market decline of at least 20 percent from their highs.

“We had years of low volatility and rising markets, and this virus crisis made it all come to an end at once,” said Kathy Jones, chief fixed-income strategist at the Schwab Center for Financial Research. “There is no endpoint in site, and that’s causing a degree of panic because people are saying, ‘I just need to hold some cash.’ There will be more turmoil, but we flushed out a lot of the people who were leveraged. A lot of good things are happening to restore liquidity and order to markets.”

Markets lurched all week, but nothing signified the chaos like oil prices, which briefly dipped below $20 per barrel — unheard of in recent years. Oil prices are so low that the industry may go through a generational restructuring. Prices need to be at least in the $50-a-barrel range for companies and producing states to make a profit.