Should A Patient With COPD Ever Take Methadone For Pain

Should a patient with COPD ever take methadone for pain relief for chronic shingles or low back pain? Dose prescribed was 5 mg twice a day. After 2-1/2 days, patient has experienced some dizziness and shortness of breath. What to do now - stick it out for 72 hours, or stop the methadone? Thanks for any guidance.