LONDON (Reuters) -Central bank body the Bank for International Settlements has flagged a possible scramble for dollars could be triggered if whipsawed investors begin to unwind positions in the $113 trillion FX swap market amid U.S. volatility. The BIS recently estimated that funds and other non-bank financial firms had more than $80 trillion in FX swaps - money borrowed in the U.S. currency with the promise to pay it back at an agreed exchange rate at a later date. The issues come if investors suddenly rush to unwind these positions, the head of the BIS' monetary and economics department, Hyun-Song Shin, said in a lecture at the London School of Economics.