Notwithstanding the chaos in Greece and currencies, please take a look at the blue lines on this chart of SPX, the S&P500 index (SPY ETF).
Notice the drops marked by the blue lines) happened right around the 18th/20th of both October 2009 and January 2010. This happens to be related to earnings season. The reason could be that that markets having risen so much were quite overvalued, and the earnings or guidance disappointed because they had been compared to the previous earnings when the markets was recovering from the 2007/2008 crash.
In other words, positive surprises will be harder and harder to come by. Given that the markets are even more overvalued now, there is reason to expect similar behavior.
In the current earnings quarter that would now be April.