Do I Need To Withdraw From Oxycodone In A Facility?

Do I need to withdraw from oxycodone in a facility? How long does withdrawal take ? My doctor wants to help me by switch me to methadone. Can I become addicted to that? I could not breath on synthetic marijuana pills. Is there a big chance that could happen with methadone? I have asthma and COPD among other ailments that cause significant constant pain. Please answer me.