Stock indexes on Thursday gave back all of the big gains from the previous session as worries about Europe’s economic situation intensified. The Nasdaq dropped 2%, while the S&P 500 lost 2.1%. The IBD 50 flopped 2.6%. Volume fell across the board. Europe took over the franchise of anxiety Thursday on a report that Germany’s exports fell 5.8% in August, the biggest drop since January 2009.