The Dow Jones Industrial Average fell 4.6 percent on Monday, and it’s down 8.5 percent since its high point on January 26.
That means stocks are now cheaper, but the value of retirement and investment accounts has dropped - making Americans poorer, at least on paper.
Some market watchers fear the US could be on the brink of recession, but not everyone agrees.
"In reality it feels that way, but we can't say it's a repeat of 1987, investors need to be calm, look at the whole picture which remains quite strong, going into a period of uncertainty and volatility missing from the market for a long time," Peter Cardillo, chief market economist in First Standard Financial Market told Al Jazeera.
While traders dumped everything from energy to finance and tech stocks, the US president, Donald Trump, said nothing.
Just last week, Trump spoke about the stock market's strength. But in Cincinnati he was celebrating tax cuts - and accusing congressional Democrats of trying to sabotage the economy.
On Monday, Jerome Powell was sworn in as the Federal Reserve Chairman, replacing Janet Yellen. She has been criticised for not raising interest rates quickly enough to curb inflation.
But now economists will be watching how Powell keeps the US economy humming, and investors from panicking - a difficult test in his first days on the job.
Al Jazeera's Rosiland Jordan reports from Washington, DC.