What is the term for the physical response to an immediate threat?

The term for the physical response to an immediate threat is referred to as an autonomic response. This type of response is part of the body's autonomic nervous system, which automatically prepares the body to react to dangers without conscious thought. It can include physiological changes such as increased heart rate, rapid breathing, and the release of adrenaline, all of which occur to prepare a person for "fight or flight" scenarios.

While concepts such as 'survival instinct' and 'combat readiness' are related, they focus on broader aspects of human behavior and psychological preparedness rather than the immediate physiological changes. A 'stressor response' encompasses a wider array of reactions to stressful situations, not limited to the immediacy of a threat. The autonomic response specifically highlights that rapid, involuntary nature of reacting to an immediate danger, making it the most accurate term in this context.