First point to note is that most of the news is about “the Dow” and almost none of us invests in the Dow. What matters to me is not what happens to “the market” but rather what happens to the stocks that I own.
Usually these fears come from news media talking heads who have nothing else to talk about. So they talk about “the market”, its history compared to something or other, or some textbook theory, etc, etc. Most of it is worthless and is best ignored.
When markets get nervous, I do notice, and my usual strategy is to trim the most speculative holdings, and keep the quality holdings. They might get thumped but most will recover in reasonable time frame. Worrying about the future is a waste of time. Respond to the numbers when they happen.