Both Indian indices, Sensex and Nifty, continued their downward slide on Wednesday, extending losses from the previous session.Sensex tumbles 796 pts to settle at 66,800.84; Nifty tanks 231.90 pts to close below 20K level at 19,901.40The BSE benchmark Sensex tumbled nearly 796 points to close at 66,801. The Nifty index tanked 232 points to slip below the 20,000-mark.