The Dow is long right now, and I would say probably safe to go long to 19000. I would set a stop loss around 16500. I expect a turning point where the market will move laterally within the next 3 quarters or so. As of the last closing, the SMI is pointed up.
It is certainly possible. Few people really think of any security in a 100 year timeframe. Movement within the envelope you describe tends to deflect from the center line, however, and the magnitudes of the "big crashes" are relative. Lateral movement away from the centerline is really expected at this point in time, by this analysis.