Sensex at the Bombay Stocks Exchange was trading 84 points down at 18,224 points a shortwhile ago. Extending losses for the third straight day, the Sensex tanked over 325 points to dip below the 18,000 level in the early trade today, to 17,982 points. The fall is attributed to sustained selling, as rupee plunged to fresh lows amid a weakening trend overseas. The 30-share index had lost over 1,060 points in the previous two sessions.The Nifty was also trading 22 points down at 5,393 points.