The BSE benchmark Sensex was trading 55 points in red at 18,619 in noon trade. Earlier, the Sensex fell by almost 75 points in opening trade today due to increased selling by participants. The 30-share index, which had lost over 129 points in the previous session, fell by 0.39 per cent to 18,600.The Nifty at the National Stock Exchange shed 17 points, to 5,658.