US government bonds recorded their worst month in four years as 10-year Treasury yields surged over 50 basis points in September to reach 5.3%, the highest level since 2007. The unprecedented sell-off in the $32 trillion market has triggered a self-reinforcing feedback loop, with rising yields forcing funds to liquidate Treasuries and driving prices lower. JPMorgan portfolio manager Priya Misra warned that the vicious cycle could persist as investors remain reluctant to intervene amid the momentum. Market participants describe the current environment as a "freight train," noting that mandatory fund selling continues to accelerate the downturn in the world's most critical debt market.