The BSE benchmark Sensex fell by over 129 points in opening trade today . The 30-share barometer, which gained 117.13 points in the previous session, fell by 129.67 points, or 0.71 per cent, to 18,184.66 in the first few minutes of trade . Similarly, the wide-based National Stock Exchange Nifty index slid by 38.65 points, or 0.72 per cent, to 5,477.15.