This post originally appeared on RealMoney on April 28 at 9:10 a.m. EDT. To see Ron Insana's post's in real-time, you can click here to join RealMoney.The Mamas and the Papas thought, some four decades ago, that Mondays could not be trusted. They sang about how every other day of the week was fine (yeah), but not Monday. And we know why: The weekend was over. It was back to the grind, the salt mine, the office. But in this secular bear market, that all changed. In the last year, Sundays appear to be the riskiest day of the week, for Wall Street if not for Main Street. In the 25 years that I have participated in the financial markets, I can't recall a time that the "day of rest" was so fraught with risk.