This is not that unusual.
Some perspective: Since the Dow index inception in 1896, it has only increased seven or more years three times; this year, it's on a six year winning streak, so it was kind of overdue. It also drops about 5% in a day every couple of years. In 2002-2004, it dropped 6%, 7% and 17% for the year. In 2008, it went down 34%. This year it is down 10%.
Short-term shocks like this are common in the stock market and long-term bears are possible. Now is a good time to see how you react. If you rush to sell or buy short, it probably means your allocation is too high in stocks.
(Whatever happened to 100 minus age as a good rule of thumb or starting point for stock allocation? Even that may be too rich for many.)