The Sensex at the Bombay Stock Exchange remained weak in afternoon deals, and had fallen 81 points, or 0.4 percent, to 20,770 a short while ago. Earlier in the morning, the Sensex had declined 91 points, or 0.4 per cent, to 20,760, on sustained selling by funds and retail investors, amid weak regional bourses. The Sensex had lost 320 points in the previous three trading sessions. Stock markets in Japan, China, Taiwan, Hong Kong, Singapore and Indonesia had declined between 0.1 percent and 2.3 percent, today, after a gauge of China's services industries fell, signaling that growth may slow in the world second-biggest economy.