Sympathetic nervous system 

The sympathetic nervous system is part of the autonomic nervous system responsible for the “fight or flight” response.

It increases heart rate, blood pressure and alertness in response to stress. In pain medicine, sympathetic overactivity can worsen or even maintain pain, especially in conditions like Complex Regional Pain Syndrome (CRPS), where abnormal sympathetic activity contributes to burning pain, color changes, and swelling.

Therapies targeting the sympathetic system — such as sympathetic nerve blocks, medications, or biofeedback — aim to restore balance and reduce pain.