The megaphone pattern in the U.S. stock market typically presages a major decline or full-blown crash.
Market observers have long noted that increasing volatility presages market crashes. If you glance at a chart of September-October 1929, just before the crash that started the Great Depression, you will note the same sort of manic swings of euphoria and fear that have characterized the U.S. stock market over the past few months.
Not only are the swings increasing in amplitude, the time between each move up or down is decreasing. Think of a series of wind storms that grow increasingly more violent even as the time between storms diminishes.