Greece is in a bad situation. They don't have enough revenue to pay their expenses, and the effected interest groups does not understand that the only alternative to merely promising to cut expenditures (to get IMF loans), is actualliy cutting expenditures. Bad news, but Greece's GDP is only 3% of the US, so it's not that important.
But then around 2:45 EST the market started a free fall. Electronic exchanges like Arca became frozen, unable to send orders, and without the electronic market makers the prices basically had no support. Some big stocks like Procter & Gamble and Citigroup had bid-ask spreads effectively at 10%. It wasn't clear if the Mayan doomsday had been accelerated, Israel was in a war, who knew? Later it was mentioned this was caused by some poor guy at Citi who sold $16 Billion worth of S&P futures, not the $16 Million he was supposed to trade (his performance review this year should be leaked to the internet as comedy gold) Some exchanges are going to cancel some silly trades, but they had to have moved more than 60%, meaning a lot slightly less ridiculous trades are going through.
Just another reminder: if the market is going bananas, stand back. Retail traders get screwed in these environments, but only the impatient ones. Don't think you will get out first, the institutions are way ahead of you.