On Wednesday afternoon, just after the close of the market, the US Dollar, the 
world's reserve currency flash crashed. This is how the WSJ described the move:

In the latest episode Wednesday, a message from the U.S. federal reserve that it is in no hurry to raise interest rates caused a big slump in the dollar, which has run up a huge rally so far this year. The euro surged more than 4% against the buck, its biggest jump in a single day in 15 years, according to Deutsche Bank. Early on Thursday, the European currency resumed its slide.

The sheer speed of the round trip in the euro-dollar exchange rate—the world's most heavily traded currency pair—left traders and investors reeling.

We profiled the staggering move in real-time 
world's reserve currency flash crashed:

Again, this is the world's reserve currency, not some two-bit backwater currency pair. It was, also, a stunning, unheard of event.

This is how the rest of America's traders saw itWSJ described :

“I haven't seen anything like it since the financial crisis,” said Paul Lambert, head of currency at Insight Investment, which manages $480 billion of assets.

Traders said Wednesday's move brought back memories of January's surge in the Swiss franc, when the currency climbed more than 40% after the Swiss central bank abandoned its policy of capping the franc's strength against the euro. For a few minutes on Wednesday, the lack of dollar buyers caused a short-term freeze in electronic trading platforms, according to a New York-based trader at a major currency-dealing bank. “There was a lot of shouting on the desk, a lot of nervousness,” the trader said.

“The dollar has been experiencing fastest pace of ascent in 40 years. Our long-term outlook for the euro is still lower, but risk here is for a decent pullback,” said Matthew Cobon, head of interest rates and currencies at Threadneedle investments in London, which has a total $54.3 billion of assets. Mr. Cobon had bet on a bounce back for the euro ahead of Wednesday's Fed meeting.