The market had a minor freak-out to start September, with shares of Nvidia getting hammered. Investors want to know what’s coming next—but things aren’t looking so great in the near term. Pile on what some investors believe are extended valuations—the S&P 500 trades at about 21 times estimated earnings, up from about 17 times five years ago—plus the fear that September is a bad month for stocks, and it all adds up to increasing anxiety.