1.
Why does prolonged stress often result in an increase in illnesses?

a typical stressful response is an increase in heart rate, and your blood vessels constrict. this is one of the reasons that chronic stress is associated with cardiovascular disease.

Interlink between the brain & the immune system. In fact, the psychological stress can induce the acute phase response commonly associated with some infections and tissue damage, and it increases the levels of the circulating cytokines and of the various biomarkers of inflammation.