The BSE benchmark Sensex was trading 143 points down at 15,928 points a shortwhile ago. Sensex dipped below the 16,000 points level in early trade today by losing 232 points on heavy selling by funds and retail investors, tracking weak global markets. The 30-share barometer had closed higher by 40 points in yesterday's session.National Stock Exchange index Nifty was also trading 44 points down at 4,826 points a shortwhile ago.