Wall Street plunges over 600 points on Fed decision; energy sector weighs on S&P 500

US equities sold off sharply after the Federal Reserve's policy decision, with the Dow falling more than 600 points. The energy sector is cited as a heavyweight drag on the S&P 500, suggesting a risk-off reaction to the Fed's stance. The exact nature of the Fed's decision (hike, hold, or guidance) is not specified, but the market move indicates a hawkish surprise or disappointment.