Losing its initial gains, the BSE benchmark Sensex was trading 139 points down at 19,859 points a shortwhile ago. It dropped 133 points in late morning trade after hitting the 20,000 level after fresh selling in banking, auto, IT, tech and metal stocks. It gained 55 points in early trade today on buying by funds and retailers.The wide-based National Stock Exchange index Nifty was also trading 38 points down at 5,875 points.