The S&P 500 Index dropped 9.5 percent yesterday in its worst day in more than three decades. It joined the Dow in a bear market, as it's now more than 20 percent from its recent peak.
The Dow also suffered its worst point drop ever and the biggest percentage decline since 1987.
Things got so bad that for the second time this week, a market-wide circuit breaker was triggered to prevent stocks from a free-fall. Trading was halted for 15 minutes shortly after the market opened, following an initial 7 percent drop in the S&P 500.
The Dow is off 18.03 percent so far this week. It wouldn't take much of a drop today to book the worst weekly decline for the index — which turns 124 years old on May 26 — if it surpasses the 18.15 percent drop in the week ended October 10, 2008, at the height of the financial crisis that ushered in the Great Recession.