Market also went to dog house in summer 2015 to early 2016

The primary driver was growing concern about China's economic slowdown, oil price collapse ($20+ per barrel in January 2016), end of QE and speculation about interest rate hikes. 

From August 18-21, 2015, the Dow fell 1,300 points.  We were having our annual summer vacation at the beach.  The mobile signal was so weak, I drove to the town to put the buy orders.