Losing its initial gains, the BSE benchmark Sensex was trading 145 points down at 19,853 points a shortwhile ago. It dropped 145 points in late morning trade after hitting the 20,000 level after fresh selling in banking, auto, IT, teck 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 42 points down at 5,872 points.