Sub-threshold DRG Stimulation vs Sham in Established Responders

The goal of this clinical trial is to learn if sub-threshold dorsal root ganglion (DRG) stimulation provides pain relief beyond placebo in adults with chronic neuropathic pain who already have an implanted DRG stimulator. The main questions it aims to answer are: * Does sub-threshold DRG stimulation reduce daily pain intensity compared with sham stimulation? * How does sub-threshold stimulation affect sleep, mood, and daily activity? Researchers will compare active sub-threshold DRG stimulation to sham (device switched off) to see if stimulation has a genuine effect on pain and wellbeing. Participants will: * Be randomly assigned to receive either active sub-threshold DRG stimulation or sham stimulation for 5 days, followed by the opposite condition for another 5 days. * Complete short electronic diaries twice daily about their pain, sleep, mood, and activity. * Attend study visits for safety checks and assessments.