Prolonged stress can increase one's vulnerability to illness in part because recurrent autonomic nervous system arousal leads to

Stress can impair the ability of the immune system to respond to hormonal signals that destroy inflammation. Stress can weaken the immune system and suppress the cellular immune function. Stress can prolong SNS activation and prolong the release of cortisol damages in the hippocampus. The SNS is part of the autonomic nervous system. Chronic stress can cause wear and tear on the autonomic nervous system.