Snapping two-days of gains, the Sensex at the Bombay Stock Exchange dropped 142 points, or 0.8 percent, to 18,328, today, on profit-booking by investors, amid rising crude oil prices, and falling Asian and European markets. The Nifty at the National Stock Exchange shed 37 points, or 0.7 percent, to 5,494.Stock markets in Japan, China, Hong Kong, Singapore and South Korea fell between 0.5 percent and 1.5 percent.