When there is stress but no actual danger, a person can be left feeling restless and irritable. This is partly because adrenaline causes the body to release glucose , raising blood sugar, and giving the body energy that has no outlet. Many people find it beneficial to "work off" the adrenaline rush after a particularly stressful situation. In the past, people handled this naturally through fighting or other physical exertion, but in the modern world, high-stress situations often arise that involve little physical activity. Exercise can use up this extra energy.