The sympathetic nervous system reaction is normal and necessary for protecting us from potential threats. Stress becomes harmful when the sympathetic response cannot be turned off and the body cannot return to the parasympathetic rest/digest state. Chronic stress keeps the cortisol levels elevated and never return to baseline, causing insomnia, depression, or anxiety or causing the development of digestive disorders like constipation or diarrhea. People who are chronically stressed don't handle acute stress very well.

How do our emotions affect the body’s stress response? Could this lead to disease?

Emotional wellbeing is closely connected to human physiology and TCM sees negative emotions as pathogenic factors. So when our thoughts and emotions become uncomfortable the brain responds by activating the sympathetic nervous system fight/flight response. The HPA feedback loop, or hypothalamus-pituitary-adrenal loop releases stress hormones, such as cortisol, that can then negatively affect our body's homeostatic balance if they are not turned off.

Homeostasis is a term used to define a well-working body; everything is functioning, as it should. Homeostatic imbalance weakens our immune system (more susceptible to getting sick), changes our sleep patterns (our essence is not anchored), leads to heart disease (in TCM only the heart organ "feels" emotions), damages endocrine health and chemically changes the wiring of the brain reducing our ability to think clearly and problem-solve. Hypertension, cardio-pulmonary disease, gastrointestinal disorders, immune system problems, even cancer has been linked to this pathological process. Disease can be caused by stressful emotions.