Sensex fell from its previous close of 79,724.12 to 78,975.99, a drop of 748.13 points or 0.94 per cent; Nifty opened slightly higher at 24,315.75 from its previous close of 24,304.35 but slid to 24,080.15, down 224.20 points or 0.92 per cent by 9.40 AM