The drop pushed the S&P's decline from its September highs to 6.5%, two-thirds on the way to a technical correction.

However the relatively stability at the index level has masked turmoil among individual names where some 1,256 stocks hit 52-week lows, while only 21 establishing new highs.

More concerning, and a testament to the tech-heavy leadership of the market concentrated amid just a handful of stocks, is that while the broader S&P 500 index has yet to enter a correction, more than three quarters of all S&P stocks - or 353 - have already fallen more than 10% from their highs. Worse, of those, more than half 179 have already fallen by 20% or more from their highs, entering a bear market.