Because of this, our brains and bodies are wired to be overly sensitive to threats. This phenomenon is often referred to as the "smoke alarm" principle, based on the idea that it is better to be awakened 10 times in the middle of the night by a false alarm than to sleep blissfully just once while your house burns down around you.
However, not all threats are created equal when it comes to activating "smoke alarm" pathways in the brain and body that evolved to help us cope with environmental dangers.
Read the entire article at http://www.cnn.com/2013/04/17/health/raison-terror-danger/index.html?hpt=he_t5
Read about Charles Raison at http://cals.arizona.edu/fcs/faculty/Charles_Raison