My vote is that you will feel funky when the stuff is leaving your system. And once it is out you will be sick for maybe a week then rebound and the next week will still be a big lingering of not feeling right and by the third or fourth week your going to be eating, using the restroom mannerly, and sleeping semi decently, and smiling.
I am all ears to your story post anything and write away. You may get off easier than you think in terms of withdrawal, dont fear it to much please - it truly does not help , only looking it in the eyes does. I'll be lurking waiting to hear how your doing. I have a slight feeling you might feel like crude for a week and then feel much better after that if your treatment center does any aftercare comfort meds etc and fun things to occupy the mind.
Best of luck! Rooting for you.