There’s the sympathetic nervous system that puts the body in high alert mode—raises body temperature, heart rate, blood pressure, blood sugar, respiration, the works—and primes us for action. And then the parasympathetic system cools everything down, letting the body reset and repair. Together they make up our “autonomic nervous system” that either controls or at least strongly influences the physiology that operates below the level of conscious awareness. If we’re young and healthy, the sympathetic and parasympathetic systems toggle back and forth almost effortlessly, responding to the day’s challenges and recharging at night. But as we get older, we tend to get stuck in high gear – the sympathetic system dominates – and we pay a price for that. The parts wear out; we generate more metabolic waste. We can’t sleep properly, compounding the damage. Net result: we age faster.