If your therapist was using iontophoresis and not muscle stimulation, this can cause temporary numbness as you describe.
Lyme disease can cause many muscle, joint and nerve pains. It is certainly worth getting a rheumatologist consolation to help understand if this is affecting your outcome.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.