LONDON, Jan 21 (Reuters) - European shares sank 5.6 percent by midday on Monday, threatening their worst one-day fall since the attacks of September 2001 as investors rattled by the spectre of a U.S. recession dumped stock across the board. At 1204 GMT, the FTSEurofirst index index of top European shares was down 5.1 percent at 1,289.42 points, having earlier hit 1,280.94, a level not seen in eighteen months. http://www.reuters.com/article/marke...0080121?rpc=44