The Sensex which opened 166 points in red, recovered some of its ground and was trading at 37 points down to 18,864. The 30-share barometer, which had surged by over 470 points in the last six sessions, fell by 0.87 per cent, to 18,736 in opening trade today.The Nifty at the National Stock Exchange fell by 18 points to 5,741.