The 'fight-or-flight response" can be healthy and/or life-saving; it worked fine for cavemen. When you're in danger, hormones equip you to deal with it.
The same hormones trigger processes that can be unhealthy. Stress is good if it gets you 'psyched' up for an exam, but bad if it stops you sleeping the night before. As people adopt more sedentary life-styles, and do stressful jobs that stimulate the hormones but don't provide the relief of physical 'fight-or-flight', the problem has been getting worse (and getting worse more quickly).
That tension between good and bad accounts for the apparent inconsistencies you've noticed.
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