Posting its biggest single-day fall in eleven weeks, the Sensex at the Bombay Stock Exchange plunged 406 points, or 2 percent, to close at 20,229, today, as global markets fell, on fresh fears that the US Federal Reserve will begin tapering its economic stimulus earlier than expected. The Nifty at the National Stock Exchange dropped 124 points, or 2 percent, to 5,999.Stock markets in China, Hong Kong, South Korea and Singapore all ended with losses.