When our Pleistocene ancestors saw movement in the tall grass, their brains released stress hormones, increasing heart rate and respiration, dilating eyes to increase awareness and diverting blood from the digestive tract to arms and legs. The body was preparing to fight, or run very fast in the opposite direction. Carnivores in the tall grass are not a problem today, but there is plenty to fear. It's a lousy feeling that hits you right in your blood-deprived stomach. If anxiety persists due to war in Iraq, terrorists, bird flu, arctic melting, gas prices, or Rumsfeld, the brain switches to a long-term strategy. The hypothalamus, which controls emotion, tells the adrenal cortex to release cortisol, another stress hormone that raises blood pressure and increases blood glucose levels. New findings from Harvard Medical School links cortisol levels directly to depression for the first time. You're being manipulated by your hypothalamus. You can try to persuade your brain that there are no tigers, or take antidepressants that boost serotonin, another hormone that constricts blood vessels, countering the cortisol.
I have to have my cortisol level checked. And I have to have my serotonin levels boosted--without all the intolerably nasty side effects of SSRIs.