If, indeed, you haven't been able to step out of the way of these events, here's some advice to follow before the next downturn comes along (and, by all accounts, the next one may be sooner rather than later). First, don't make any knee-jerk reactions. If you think you can stave off further loses with a couple of trades you're fooling yourself (and probably selling at the worst possible time). If you are living off your retirement account, you may want to reconsider how much you are pulling out of it for household expenses. At least one study has shown that you can severely cut into the life of a retirement account by tapping it at its lowest balance.

You should also check to see how your funds react to these big downturns. We like the idea of a diversified portfolio in these situations. In concept, at least, a diversified portfolio should smooth out any wild rides. If, say, your portfolio of large-cap stocks takes a sharper dive than the overall market you may want to re-evaluate it, especially if you realize you can't stomach these ups and downs.

Finally, every investor needs to sit down after days like these and do a gut check. Once the dust settles there will be some prime buying opportunities for those with cash and the nerve to put it to use... Indeed, last week we polled some fund managers about where they saw bargains in the financial-services industry. This morning one of our interviewees, Anton Schutz, who runs Burnham Financial Services (BURFX), reiterated on CNBC what he told us last week: 'There will be great opportunities.'"