Falling for the fifth straight session, the Sensex at the Bombay Stock Exchange lost 107 points, or 0.6 percent, to 16,776, on sustained selling by investors, amid weak Asian markets, today. The Sensex had lost over 680 points in the past four trading sessions. The Nifty at the National Stock Exchange fell 38 points, or 0.8 percent, to 5,030.Stock markets in Japan, China, Hong Kong, South Korea and Singapore dropped between 0.2 percent and 2.5 percent.