As has already been discussed many times since March 2009 and also documeted in a working paper (S&P 500 returns revisited), we expect the S&P 500 stock market index to be gradually decreasing at an avearge rate of 46 points per month. In this post on S&P 500 (01/05/2010), we put the closing level of S&P 500 in May 2010 at 1132 (miscalculation, should be 1142). The actual closing level was 1090 (-97 relative to April 2010), i.e. 42 points below the predicted one. One could expect that kind dynamic "overshoot" in the beginning of a new trend. Same purely emotional effect was observed in March (+69) and April 2009 (+74), when the S&P 500 was increasing much faster than the average rate for the whole period of the rally between March 2009 and April 2010.
So, one might not exclude that the panic of May 2010 will last another month and the closing level of S&P 500 in June will be below 1095, as would be predicted by the rate of -46 points per month starting with 1187 in April 2010. By the end of the summer, the fall will likely decelerate. But the overall downward trend will continue and extend into 2011.