Fears that policymakers are running out of options to revive a slowing global economy sent investors out of stocks and into the safe haven of the dollar, the yen and US Treasurys.

A key trigger for the reversal of investor sentiment was Tuesday's policy statement from the Federal Open Market Committee. Although the Fed resolved to deliver modestly more liquidity to the market by reinvesting proceeds from its mortgage-backed securities holdings, investors are now wondering whether this will be enough given how much the Fed downgraded its assessment of the economy in that same statement.