Physiological mechanism Experience (symptom)

Stimulus-independent pain (spontaneous pain)
Development of and (or) increase in spontaneous neural activity)

Pain in response to a stimulus that does not normally produce pain (allodynia)
Reduction in the neural threshold for activation9

Increased pain from a stimulus that normally provokes pain (hyperalgesia)
Increased neural response to repeated, fixed-intensity, C-fibre strength stimulus72

Spread of pain to adjacent, undamaged tissue (secondary hyperalgesia)
Enlargement of neuronal receptive fields9

Spread of pain to distant body regions (remote hyperalgesia)
Injury-induced unmasking of previously ineffective synaptic connections37

Spread of pain to distant body regions (remote hyperalgesia)
Cross-system, viscero–visceral interactions within the central nervous system40

Mirror-image pain (allochiria)
Ipsilateral injury-induced, contralateral peripheral neurite loss49

Katz J, Rosenbloom BN, Fashler S. Chronic Pain, Psychopathology, and DSM-5 Somatic Symptom Disorder. Can J Psychiatry. 2015 Apr;60(4):160-7. doi: 10.1177/070674371506000402. PMID: 26174215; PMCID: PMC4459242.