Snapping a six-session winning streak, the Sensex at the Bombay Stock Exchange dropped 56 points, or 0.3 percent, to 18,846, on profit-booking by investors, amid falling regional bourses, today. The Sensex had gained 470 points in the last six trading sessions. The Nifty at the National Stock Exchange fell 21 points, or 0.4 percent, to 5,739.Stock markets in Japan, China, Hong Kong, South Korea and Singapore slumped between 1 percent and 2.4 percent.