My Cytomel dose was backed off by 2/3 up until about 2 days before taking the iodine.
My surgeon originally put me on 50 mcg Cytomel, same as you, but I felt like shit. Exhausted all day except for a few hours in the morning. Even worse was this mental fog/confusion I was experiencing. I had to slog through it for a couple of weeks and then my blood work showed my TSH levels through the roof, so the surgeon agreed 50 mcg was nowhere near enough for me, and raised me first to 100 and then to 150 mcg. On 150 mcg I felt like my old self again.
Well, when I met the endocrinologist referred by my surgeon, the first thing I told him was that I was going to be useless during the low-iodine diet phase if I go off Cytomel completely. He was surprised I was not experiencing hyper-thyroid symptoms on 150 mcg (he said that's the max dose), but I wasn't. No rapid heartbeat, no hand shaking, no trouble sleeping. So, anyway, he backed me back down to 50 mcg. Like I said, I was exhausted, but I'm sure it would have been worse with nothing in me at all.
You may not feel as terrible as I did on a low to no-dose of Cytomel, so you may do fine for a couple of weeks on 0. I think it all depends on the individual. But if you do feel like shit, tell the doc about my experience and how a lower dose was still OK.
The main thing they look for before they give you the radioactive iodine is that you have a very high TSH level (i.e., you body is starved for thyroid hormone) right before you get the radioactive iodine treatment. I was warned that if my TSH level wasn't high enough a few days out, it would delay me getting the treatment and I would also have to go off the Cytomel. Well, in my case, it all worked out fine.
Also, as DianaB pointed out, I AM back to normal! I just take Levoxyl (aka Synthroid) now, 175 mcg. At first that dose was too low, but I somehow adjusted and feel normal energy levels. I'm also getting leaner and just hit some new PRs in the squat and deadlift, so all is good.
I figure the scar makes me look tougher, too. Like I won a knife fight despite getting my throat slit, LOL.
BTW, one piece of advice about thyroid medicine no one told me about initially... Take it on an empty stomach. I.e. wait at least 30 minutes, and preferably 45, before you eat breakfast. Second, if they have you taking Calcium (my parathyroid was temporarily affected by the surgery), then make sure you take your calcium at a different time of day. Calcium will interfere with the absorption of the replacement thyroid hormone.
Best of luck to you. You'll pull through this and be fine.