Panic attacks are periods of intense fear or apprehension that are of sudden onset and of relatively brief duration. Panic attacks usually begin abruptly, reach a peak within 10 minutes, and subside over the next several hours. Often, those afflicted will experience significant anticipatory anxiety and limited symptom attacks in between attacks, in situations where attacks have previously occurred. The effects of a panic attack vary. Some, notably first-time sufferers, may call for emergency services. Many who experience a panic attack, mostly for the first time, fear they are having a heart attack or a nervous breakdown. Experiencing a panic attack has been said to be one of the most intensely frightening, upsetting and uncomfortable experiences of a person's life and may take days to initially recover from. Repeated panic attacks are considered a symptom of panic disorder. Screening tools like Panic Disorder Severity Scale can be used to detect possible cases of disorder, and suggest the need for a formal diagnostic assessment.

Sufferers of panic attacks often report a fear or sense of dying, "going crazy," or experiencing a heart attack or "flashing vision," feeling faint or nauseated, a numb sensation throughout the body, heavy breathing (and almost always, hyperventilation), or losing control of themselves. Some people also suffer from tunnel vision, mostly due to blood flow leaving the head to more critical parts of the body in defense. These feelings may provoke a strong urge to escape or flee the place where the attack began (a consequence of the sympathetic "fight-or-flight response") in which the hormone which causes this response is released in significant amounts. This response floods the body with hormones, particularly epinephrine (adrenaline), that aid it in defending against harm.

A panic attack is a response of the sympathetic nervous system (SNS). The most common symptoms may include trembling, dyspnea (shortness of breath), heart palpitations, chest pain (or chest tightness), hot flashes, cold flashes, burning sensations (particularly in the facial or neck area), sweating, nausea, dizziness (or slight vertigo), light-headedness, hyperventilation, paresthesias (tingling sensations), sensations of choking or smothering, difficulty moving and derealization. These physical symptoms are interpreted with alarm in people prone to panic attacks. This results in increased anxiety, and forms a positive feedback loop.

Often, the onset of shortness of breath and chest pain are the predominant symptoms; the sufferer incorrectly appraises this as a sign or symptom of a heart attack. This can result in the person experiencing a panic attack seeking treatment in an emergency room.

Panic attacks are distinguished from other forms of anxiety by their intensity and their sudden, episodic nature. They are often experienced in conjunction with anxiety disorders and other psychological conditions, although panic attacks are not usually indicative of a mental disorder.

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