Quote from Ghost of Cutten:
It's simply that sentiment got all one-way against the Euro. People were seriously talking in the summer about the Euro disappearing, not just having problems, but going back to Drachmas etc. There was a huge one-way speculative position short the euro, and there were just no more sellers left, then they got squeezed. Normally it would have just caused the market to go from 1.19 (the low) to maybe 1.30ish, but the QE news from Ben sent it up to the absurd price of 1.40+.
It's similar to all those bear market rallies in 2008 before the Lehman failure - each time the VIX got to 35-40 and fear was rampant, the market bounced 10% or so, and it was only once the whole system started wobbling that people stopped buying the dips and full-blown panic selling set in.