The dollar’s slide intensified this past week, raising investors’ concerns that a decline initially greeted as a boost for the U.S. economy and companies could become more unpredictable and volatile if the recent pace of the currency’s fall continues.

The U.S. currency had its worst week in more than three months and has now lost 9.1% in 2017, reaching its lowest level in nearly 2½ years. Doubts over whether the Federal Reserve will be able to deliver another interest-rate increase this year, rising tensions with North Korea and hurricanes threatening the southeastern U.S. have accelerated those declines in recent days.

Investors and policy makers have welcomed a weaker U.S. currency after a four-year rally took the dollar to its highest level in nearly a decade-and-a-half, punishing earnings at multinational corporations and hurting U.S. exports. A falling dollar makes U.S. goods more competitive abroad, a key policy objective of President Donald Trump. The boost to growth provided by a weaker currency also gives the Fed more room to raise interest rates.

But if the dollar’s value continues to erode at the same pace it did in the past week, that weakness may mean new difficulties for the U.S. and global economies.

A sharp drop by the dollar could shake faith in the U.S. economy, elevating concerns about lofty stock-market valuations and complicating the Fed’s monetary-policy strategy. If the currency falls far enough, fast enough, it could increase fears that inflation will accelerate beyond the moderate pace anticipated by policy makers and investors.