The Sensex was trading 426 points down at 18,131 points a shortwhile ago. Snapping 3-day winning spree, the 30-share index today tanked over 221 points in the early trade on fresh selling with banking, realty, metal PSUs and oil and gas sector stocks leading the fall. Sensex had gained over 652 points in the previous three sessions.Similarly, the wide-based National Stock Exchange Nifty was also trading 128 points down at 5,349 points