This is taken from a recent article written by Martin Armstrong and I think very germane to what has occured here.
"In order for markets to move, the internal mechanism is always like a pendulum. Whenever a market becomes excessively bullish, the internal energy is then set so that the market once it reaches the point of maximum ENTROPY, has become tired lacking a new crop of bulls to come in and take it up further. This is the point when we see the SMALLEST AMOUNT OF SELLING PRESSURE AND CAUSE THE GREATEST AMOUNT OF CHANGE. It is NEVER that some huge short player has entered the market and forces it down. What happens is everyone is long expecting to be rich counting their profits but lack further buying capacity. Thus, the SMALLEST amount of selling pressure can then move the mountain of tired longs forcing the weak longs to now sell shaking the confidence of even the steadfast. The sharp increase in selling pressure is not conspiracy theories generated to create some fictitious group so powerful to explain why the analyst is wrong".