The Sensex is now trading down 98.46 points at 18510.35.The Sensex fell sharply by over 192 points in opening trade today. This follows foreign funds and retail investors booking profits made during the previous two sessions, taking cues from weak global markets.Profit-booking by speculators after two sessions of gains also dragged the Sensex down.Stocks of banking, realty, metals and auto companies suffered the most in the fresh sell-off.The wide-based National Stock Exchange Nifty index is trading down by 28 points, to 5,563.