We've seen the quick plunge, then rebound scenario happen so much since late October really (only difference is that time had a deeper correction) but I think this one tops them all if we manage to finish the day with all 3 of the major averages at record closing highs.
If this continues to early November (which I do have my doubts about as I've been eyeing September if tech fully reporting doesn't stop the Nasdaq-100 shortly), the "quick plunge, then rebound" deal is going to be the story of the full 12 months.
I've been getting tricked by it lately. Shame on me. I think what should probably be the best gauge is to keep an eye on the 50 day for the S&P. It's had multiple fast pullbacks down there, but hasn't stayed down there for long. Stay lower than it for more than just a day or two or keep selling while under it and that'll probably be the moment that you see something more like that pullback in September last year.
Edit: It's not that I trade, as I've said, although I've given thought on "getting more cautious" at times and maybe hedging a little when things don't feel right.