The pupils of the eye dilate to admit more light and increase peripheral vision to scan for danger. Sensitivity to bright light, and visual disturbances may occur. The digestive system shuts down to conserve blood for the muscles. A dry mouth and nausea may result. Muscles tense to prepare for escape, but may cause spasms and trembling when action is not taken.
Thoughts are are focused on the search for the threat, maintaining alertness and vigilance.
If there is no explanation for the emergency response, thoughts of loosing control, going crazy, or dying may occur. The fight or flight response is time limited because adrenaline is metabolized by the body. When the perceived danger has passed, the parasympathetic nervous system counteracts the activation of the sympathetic nervous system, returning the body to a relaxed state. This indicates that panic disorder may be genetically transmitted. Phobic avoidance may develop as patients seek to prevent further panic attacks.