What is an involuntary reaction to an immediate danger or threat called?

The term for an involuntary reaction to an immediate danger or threat is best described as the "fight or flight response." This physiological and psychological reaction occurs when an individual perceives a threat, triggering a series of bodily changes aimed at preparing for either confronting the danger (fight) or fleeing from it (flight). The response is automatic and involves the activation of the sympathetic nervous system, leading to increased heart rate, rapid breathing, and heightened alertness, among other changes.

Reflexes, though related, typically refer to simple, immediate responses to stimuli that do not involve higher cognitive processes or the evaluation of danger, such as pulling your hand back from something hot. Conditioned responses are learned reactions developed over time through associations, while the relaxation response refers to a state of calm that counters stress responses, often requiring conscious effort to achieve. Thus, the fight or flight response accurately encapsulates the body's automatic reaction to immediate danger.