The worst jitters seem to afflict the stock markets on either a Monday or a Friday, the beginning and end of the trading week.

Friday's fall of 541.74 points in the Sensitive Index of the Bombay Stock Exchange ranks fourth in absolute terms and 12th in percentage terms.

The biggest-ever fall happened 14 months ago on May 18, 2006 - also known as Black Monday - when the index fell of 826.38 points (6.76 per cent). The trigger then was a decline in base metals prices, rising interest rates and the liquidity crisis arising out of margin trading.

The index had reported second biggest fall of 616.17 points to 12,455.37 -- or 4.7 per cent on April 2, 2007, a Monday, on fears that the Reserve Bank of India [Get Quote] would suck out liquidity leading to a rise in interest rates.

The third biggest fall was again on a Monday -- May 17, 2004 - after the United Progress Alliance led by the Congress defeated the Bharatiya Janata Party-led National Democratic Alliance.

Out of top 10 falls of the Sensex, the five falls were reported during the current year while four others came in 2006 and one in 2004.