The BSE benchmark Sensex opened over 18 points lower today. The 30-share barometer, which lost over 110 points in the previous two sessions, fell further by 0.10 per cent, to 18,366 points in the first five minutes of trade. Similarly, the wide-based National Stock Exchange Nifty index slid by 11.40 points to 5,509 points. According to market experts, the trading sentiment turned bearish on sustained selling by funds and retail investors ahead of the release of index of industrial production data later today.