1. Be patient, don't panic.
2. Buy and hold.
It's pretty much just how normal people behave when sudden event occurs in unexpected time that you wouldn't imagine before and for traders managing their emotions are becoming a chore thing to do if you want to achieve bigger profit in trading scene. It's difficult to do at first, but once you get used to it and encounters it many times, I think you can build up your patient and relieve your stress once bad thing happens.