Back to the chart; look out for the 100-day SMA line support at 24470 now, and the uptrend line support at 23700. If both of these supports failed, you should be worried. Of course, that's not to say that these supports will not break. They are still intact and the market may still come back up.
Chart: DJIA's daily chart as at Mar 5, 2018 (Source: Stockcharts.com)