Complex Regional Pain Syndrome (CRPS) is a long lasting, very painful condition. Normally, after an injury or surgery your sympathetic nervous system is activated to bring about healing and return your body back to normal.
The sympathetic nerve is activated from the message of pain that is received from the initial injury.
Due to distorted information processing, of unknown cause, these nerves continue to send the message of injury to the brain and so the symptoms of the initial injury (redness, swelling) are continually experienced.
Therefore, an abnormal healing response is demonstrated. The pain of the initial injury is felt long after the injury has taken place and usually worsens.