Dr. Hanson gives a great explanation of how your body responds to stress. Your thyroid releases more thyroid hormone, endorphins increase, sex hormones and digestive activity decrease, your liver releases cholesterol, heart rate increases, and your blood thickens. These are all positive responses to an emergency. The increase of thyroid hormone speeds up your metabolism, providing quick extra energy. More endorphins decrease your sensitivity to pain.
Digestive activity shuts down in order to divert all available energy to muscles.
Extra cholesterol provides energy in place of the digestive system. Increased heart rate pumps more blood and, therefore, more oxygen and nutrients to the muscles. Blood thickens to reduce bleeding, carry more oxygen, and fight infection. Unfortunately, modern life turns these responses into health threats. Adrenals become depleted, unable to produce more endorphins, so pain levels from migraine, backaches, and other conditions increase.