Fight-or-flight is a hair-trigger response that evolved in primitive times to prepare the body to meet imminent physical danger. The sympathetic nervous system, the emergency branch of the autonomous nervous system, takes over and all systems are Go. The adrenal glands squirt hormones into the blood stream to speed up body functions. Nerve fibers signal the smooth muscles to constrict every artery and arteriole. Blood pressure shoots up, and blood is shunted from the digestive system to the brain and muscles. Glycogen (sugar) is released from the liver, filling our muscles with energy and tensing them for action. Meanwhile, the clotting ability of blood platelets increases in preparation for a possible wound.
The problem is that this response, a legacy from pre-caveman days, can be turned on by any kind of feeling that the hypothalamus and pituitary glands interpret as negative. All too many people have such inappropriate belief systems that a letter from the IRS can trigger the same emergency stale that their ancestors would have experienced on being confronted by a saber-toothed tiger.
If we act out the fight-or-flight response by either fighting or fleeing (or by jogging, bicycling, briskly walking or doing pushups), we release the pent-up muscular tension and the other stress mechanisms swiftly fade away. But if, as is so often true in modern society, physical action is impossible, we remain tensed-up and uncomfortable and we live through the day in a state of distress.
Trying to repress a negative emotion, which means concealing or burying or denying our discomfort, only intensifies our stress. Many people live in a continuously low-level emergency state with all their stress mechanisms constantly simmering. It is these stress mechanisms—the release of adrenal hormones, tensing of muscles, and heightened clotting ability of the platelets—that set off the remaining stages in the headache process.
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