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n. a basic, intense emotion aroused by the detection of imminent threat, involving an immediate alarm reaction that mobilizes the organism by triggering a set of physiological changes. These include rapid heartbeat, redirection of blood flow away from the periphery toward the gut, tensing of the muscles, and a general mobilization of the organism to take action (see fear response; fight-or-flight response). Fear differs from anxiety in that the former is considered an appropriate short-term response to a present, clearly identifiable threat, whereas the latter is a future-oriented, long-term response focused on a diffuse threat. Some theorists characterize this distinction more particularly, proposing that fear is experienced when avoiding or escaping an aversive stimuli and that anxiety is experienced when entering a potentially dangerous situation (e.g., an animal foraging in a field where there might be a predator). Whatever their precise differences in meaning, however, the terms are often used interchangeably in common parlance. See also fright. 

Fear is a primal emotional response to a perceived threat or danger, triggering the body's "fight, flight, or freeze" response. This reaction involves the autonomic nervous system, particularly the sympathetic division, which prepares the body to deal with the threat. Here are the common physical sensations experienced during fear:

Increased Heart Rate (Tachycardia)
The heart beats faster to pump blood to essential muscles, preparing the body for action.

This can feel like a pounding or racing heart.

Rapid Breathing (Hyperventilation)
Breathing becomes quick and shallow to take in more oxygen.

This may result in dizziness or a sense of breathlessness.

Muscle Tension
Muscles tighten, particularly in the neck, shoulders, and jaw, as the body braces for potential action.

This can cause stiffness or shaking.

Cold Sweat
Sweat glands activate, leading to clammy or moist skin, especially on the palms or forehead.

This helps cool the body in case of physical exertion.

Goosebumps or Chills
A tingling sensation or chills may run down the spine, sometimes accompanied by goosebumps.

Dilated Pupils
Pupils expand to allow more light into the eyes, improving vision in dim conditions.

This may cause temporary sensitivity to light.

Dry Mouth
Saliva production decreases, leading to a dry or sticky sensation in the mouth.

Butterflies in the Stomach
Blood flow is diverted away from the digestive system, causing a churning or hollow sensation in the stomach.

Shaking or Trembling
The adrenaline surge can cause trembling in the hands, legs, or entire body.

Freezing or Immobility
In some cases, fear can cause a temporary inability to move, a "freeze" response as the brain evaluates the threat.

Numbness or Tingling
Fear may cause a feeling of numbness or tingling in extremities due to changes in blood flow.

Hot or Cold Flashes
A sudden sensation of heat or cold can occur as blood flow and body temperature fluctuate.

Tightness in the Chest
A feeling of constriction or heaviness in the chest may occur, contributing to difficulty breathing.

These physical sensations are part of the body's natural defense mechanism, enabling rapid assessment and response to threats. While unpleasant, they are vital for survival, helping individuals react appropriately to danger.