Since then, they have had their ups and downs, but eventually, the yield on the 10-year U.S. Treasury hit a high of 2.06% on March 11, right before the financial crisis in Cyprus blew up and the consensus began to shift its focus to fears over an emerging slowdown in global growth.

That backdrop set the stage for a big rally in Treasuries as investors piled back into them, sending yields all the way down to 1.63% on May 2.

In the last three weeks, however, yields have reversed violently as investors have sold bonds and are once again testing the post-low highs set in early March.

And this time, Goldman Sachs says the bond market sell-off is for real (in a note to clients titled "The Bond Sell-Off: It’s For Real").