The benchmark Dow Jones Industrial Average dropped more than 300 points Thursday, continuing a three-day streak of triple-digit swings that has investors' heads spinning. Thursday's fall was the worst point loss in more than a year and the worst percentage loss since February. It was sparked by concerns over global economic growth after Germany reported that exports dropped 5.8 percent in August. It was the biggest decline in exports from Europe's largest economy since January 2009.

"Right now, one of the main preoccupations investors have is what's going on in the international economy," said Bernard Baumohl, managing director at the Economic Outlook Group in Princeton, New Jersey. Worries about the ability of governments to control the Ebola virus and a decline in oil prices also weighed on investors. The market's so-called anxiety gauge, the CBOE Volatility Index, rose about 25 percent to 18.97. The Dow unofficially closed down almost 2 percent. It was the third straight session that the index moved up or down 200-plus points. That hasn't happened since August 2011, when it had four straight such moves.

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— NBC News, CNBC and Reuters