Benchmark indices Sensex and Nifty fell significantly from day's high to trade in the red on October 21 due to various reasons, including profit booking. At 12:19 am, the Sensex was down 406.64 points or 0.55% at 73,446.26, and the Nifty was down 164.25 points or 0.71% at 22,728. About 735 shares advanced, 3,128 shares declined, and 157 shares were unchanged. Key reasons behind market decline Profit booking emerged at higher levels as Sensex fell 1,200 points from day's high while Nifty was trading below 22,750-mark.