The Sensex at the Bombay Stock Exchange opened with a big loss of 472 points, and soon dropped more than 500 points, on Tuesday morning, as the regional bourses again tumbled, following the massive overnight sell-off in the US market, amid escalating worries about the global economic scenario. Later, in afternoon trade, the Sensex staged a dramatic bounce-back into positive territory. But it then again lost ground, and stood 183 points, or 1.1 percent in the negative zone, at 16,807, in very volatile trade, a short while ago. The brief recovery of the Sensex came after an encouraging opening of the major European bourses.