Falling for the fourth straight session, the Sensex at the Bombay Stock Exchange declined 124 points, or 0.7 percent, to close below the 19,000 level for the first time in three weeks, at 18,884, today, on concerns about economic reforms. The Sensex has now lost over 680 points in the last four trading sessions. The Nifty at the National Stock Exchange fell 52 points, or 0.9 percent, to 5,694.Stock markets in Hong Kong, China, Singapore and South Korea ended mixed.