A 38-year-old woman from Mumbai with known type 2 diabetes mellitus presents with a 6-month history of recurrent episodes of dizziness, lightheadedness, and near-syncope upon standing. Her supine blood pressure is 130/80 mmHg, but upon standing for 3 minutes, it drops to 95/55 mmHg with a heart rate increase from 72 to 78/min (blunted response). She reports numbness in her feet and difficulty with micturition. Which autonomic dysfunction best explains her orthostatic intolerance?