Volatility returned to U.S. markets, with stocks roaring back from the lows of the day to close higher after flirting with a bear market. Treasuries rose and oil slipped below $46 a barrel.
The S&P 500 and Dow Jones Industrial Average turned green in a late surge after trading negative for most of the day, with a more than 800 point swing up by the Dow in less than two hours. On top of Wednesday's 5 percent surge, it was the biggest two-day rally in the S&P since August 2015.
"It's hard to explain moves like today and yesterday and the last month," said Sean O'Hara, president at Pacer ETFs. "From a time perspective, it's a historic bull market and when you get that far into the cycle, people get more jittery."
The S&P 500 has been careening toward its worst month of the record bull run and is down about 15 percent in the quarter as everything from higher interest rates to political turmoil in Washington to concern about global growth hammer at investor sentiment.