Fight or flight is the sympathetic nervous system's acute stress response, the rapid physiological mobilization for action in response to perceived threat. Heart rate increases, blood flow shifts toward large muscles, digestion slows, and attention narrows to the immediate threat.
The response is precisely adaptive in the situations it evolved for: physical threats requiring immediate action. It is less adaptive when activated by psychological stressors, social situations, or the anticipation of future problems that do not require physical response.
Chronic activation of the fight or flight response, when it becomes the default state rather than an acute response, has significant physiological costs. It sustains the same hormonal and physiological changes that are adaptive short-term but damaging long-term.
The modern environment activates the fight or flight response through news, social comparison, work pressure, and interpersonal conflict, all situations where the response is physiologically inappropriate. The body prepares to act. There is nowhere to run.
Completing the stress cycle, through physical movement, social connection, and physiological rest, is how the system returns to baseline. Without completion, activation persists.