The symptoms include rapid heart beat, numbing or tingling sensation in the fingers, chest pain, hot flushes, breathlessness, dizziness and sweating. There is also often a feeling of impending doom, and extreme fear.

When the body is under threat, it responds by releasing adrenaline from the adrenal gland. This is part of the normal protective "fight or flight" response. The heart rate and strength increases in order to provide more oxygen to the main tissues of the body. Contraction or expansion of various blood vessels divert blood from the skin, fingers and toes to the large muscles of the body. This reduces bleeding in the case of an "attack", and may cause a feeling of coldness or numbness in the hands of feet. Breathing rate increases to exchange more oxygen to ready the body for exertion such as flight. Breathlessness, dizziness and pain or tightness in the chest may be felt. Muscles tense to prepare for escape, but may cause spasms, trembling and cramp when no action is taken. The pupils of the eyes dilate to admit more light and increase peripheral vision to scan for danger. Sensitivity to bright light may occur. The digestive system shuts down to conserve blood for the muscles, but may cause a dry mouth and nausea.

Thoughts are focused on the search for the threat, maintaining vigilance and alertness. When there is no explanation for the emergency response of the body, thoughts of going crazy, loosing control or dying may occur. Some people may think they are having a heart attack.

The fight or flight response is time limited due to adrenaline being matabolised by the body. What tends to happen in a panic attack is that the body goes into a positive feedback loop. No threat is present as such, but the fear causes a release of adrenaline. The symptoms of the fight or flee response cause more fear which causes en even greater release of adrenaline, which causes more fear etc.

In other words, panic attacks are very often (but not always) due to the misunderstanding the bodies normal reaction to anxiety and causing an even greater response of the fight or flight response.