Falling for the fourth straight session, the Sensex at the Bombay Stock Exchange declined 36 points, or 0.2 percent, to close at 20,647, today, on investor caution ahead of the US Federal Reserve's decision on its monetary stimulus. The Sensex has now lost over 725 points in four trading sessions. The Nifty at the National Stock Exchange fell 6 points, to 6,120.But stock markets in Japan, China, Hong Kong and South Korea rose between 0.4 percent and 2.7 percent, after Turkey's huge hike in interest rates bolstered risk appetite.