A stress response is the body's and mind's reaction to a real or perceived threat. The acute response addressed here changes activation, attention, emotions and behaviour during or immediately after a dangerous situation. In military isolation, evasion or capture, it can support rapid protective action; high activation can also hinder observation, memory, precise movement and decision-making. Acute stress describes the short-term pressure to which the person is responding.
Physical activation and task performance
The autonomic nervous system controls many bodily functions without a conscious decision. During a threat, its sympathetic division can increase activation: heart rate and breathing rise, muscles tense, sweating increases and energy reserves are mobilised. The response includes the release of stress hormones, including adrenaline. These changes prepare the body for immediate exertion. A fast heart rate can also result from physical work, however; its level measures neither the danger nor the ability to make a sound decision.
The effect of activation depends on the task and the individual. Moving quickly out of a threatened area requires different abilities from opening a small fastener, operating an available signalling device or weighing several possible movements. High tension can drive a gross movement while making a precise hand movement more difficult. If fingers shake or a familiar operating sequence repeatedly fails, simplify the actual task and deliberately check its critical step, where the situation allows time.
Attention, startle and memory
High vigilance can draw attention tightly towards the suspected threat. A sudden sound may then cause a strong startle while other cues receive less attention. Someone fixating solely on a suspected pursuer may miss another approach or a change in the surroundings. The strength of the alarm does not establish what caused the sound. That judgment needs the cues that can actually be perceived.
The response may appear as restlessness, hurried action, fear or anger. Other people become quiet, feel emotionally numb or lose their connection with their surroundings and the task at hand. Movement or thought processes can also falter. These manifestations do not form a fixed sequence from which the next reaction can be predicted. For immediate action, the relevant question is whether the person understands their present situation and can perform the required next step.
Under high pressure in a captivity situation, even later recognition of a person seen at close range for a prolonged period can be wrong. A strong sense of familiarity does not reliably confirm the identification. Current observation and remembered identity therefore need to be kept separate. This matters particularly for decisions based on apparently recognising a guard or another person; a familiar-looking face does not replace an identification feature that is actually available.
The next necessary action
An immediate danger that still exists determines the first step. If the person has to leave an exposed location, that necessary protective movement takes priority. Where a concealed halt is actually possible, they can briefly interrupt movement, look and listen, and assess their situation and available resources. The questions are concrete: what threat can be identified now, what has changed and what action is required next? A halt serves that observation and decision; in an exposed danger area, the same halt would create additional exposure.
The next instruction to oneself should identify one manageable, familiar action. With an available signalling device, for example, mentally organise the necessary operating sequence and its critical step instead of trying to deal with the device, movement and several other problems at once. After the action, check the actual result. Existing notes can support a familiar sequence if they are safely accessible. A companion who is present and able to act can help check an important step. Alone, the person has their own check and whatever aids are actually available.
If the situation allows a brief pause and there is no breathing difficulty, the person can deliberately notice the airflow while breathing in and out for several seconds. They then direct attention back to the specific task. This requires neither breath-holding nor a forced slow rhythm. After heavy exertion or with breathing symptoms, this brief shift of attention must not interfere with the person's need for air or immediate protective action.
Application after capture
In captivity, guards may control movement, communication and access to basic supplies. The next task a person sets themselves must fit whatever freedom to act actually remains. Where an outward action is currently impossible, they can mentally break a familiar small task into its steps or organise a specific need for supplies. If an opportunity to communicate with a fellow captive actually arises later, they can prepare the necessary short message.
Check physical warning signs
A pounding heart, rapid breathing, shaking, sweating or nausea can occur as part of a stress response. Similar signs also occur with physical exertion, injury and heat or cold exposure. Confusion, unusual clumsiness or reduced responsiveness in heat or cold require attention to possible physical illness. An injury sustained during the isolating event also has to be considered. The actual course of events, the environment and observable physical problems matter; labelling them as stress must not displace the care they require.
Threat pressure can also coincide with sleep loss and physical exhaustion. A person can feel internally alarmed while their observation or thinking is impaired. A brief awake pause and attention to breathing do not replace lost sleep. Less pounding of the heart after a break therefore does not demonstrate that every ability needed for the next action has recovered.
Military use of the term
In US military health care, Combat Stress Reaction denotes an acute response to distressing events in combat. Operational Stress Reaction covers responses to repeated or sustained operational stressors, including isolation and extreme environmental conditions. Combat and Operational Stress Reactions, or COSR, is the combined framework. For an isolated person, this distinction makes clear that a sudden threat cue and sustained stressful conditions can be different parts of the same situation.
An acute stress response alone is not a diagnosis of post-traumatic stress disorder. Startle, tension or concentration problems can persist after the dangerous event.