Traders on the floor of the New York Stock Exchange on Oct. 19, 1987. (AP)

This market drop will go down as one of the worst in history.

As of mid-morning Monday, the S&P 500 is down around 14% over the past three trading sessions. That puts it on course for its largest percentage decline over such a period since October 1987, around the Black Monday market crash, according to Dow Jones Market Data.

The tech-heavy Nasdaq Composite has fallen more than 15% over the same time frame. It is on track for its largest three-day percentage drop since April 2000, around the dot-com crash.