The signs and symptoms of chronic pain differ from those of acute pain.  Health care workers are trained to recognize and treat acute pain, which is easily recognized by hyperactivity of the autonomic nervous system - sweating tachycardia, hypertension - and the patient's grimacing, crying and anxious face.

On the other hand, patients suffering from chronic pain may exhibit few of the usually recognized symptoms of pain.  The autonomic signs are absent in chronic pain, and the patient's face may show very few signs of distress.  After long periods of unrelieved pain, the patient's face may no longer exhibit anxiety, but instead shows exhaustion and depression.  Suffering may be hidden beneath a brave, stoic face.  The lack of objective signs of chronic pain, coupled with the patient's depressed, sleepy face, often lead to a misdiagnosis or under diagnosis of pain.