Dereksister, I had Hashimoto's prior to thyroidectomy for thyCa. I didn't experience Hashi symptoms after thyroidectomy. If you are still experiencing symptoms RAI should fix them. It destroys remnant thyroid cells left in the thyroid bed and any loosed into the body during surgery.
I had to stop Levothyroxine 4 weeks prior to RAI and adopt a low iodine diet. I was prescribed Liothyronine (T3) for the first two weeks. Two weeks T3 should be enough for TSH to rise >30 for RAI uptake. It's a bit grim off meds and you should expect to feel fatigued and cold.
I had thyroid function tests as an outpatient a week before I was admitted. The RAI was administered in a capsule swallowed with water. I was quarantined for 3.5 days until radioactive levels dropped sufficiently for me not to be a hazard to other people. Visitors were not allowed to enter the room. A nurse brought meals which I collected at the door and plates and cutlery were placed in a receptacle which was collected after I left.
Take old nightwear, underwear, slippers or flip flops and toothbrush which can be incinerated or collected six months after decontamination. My hairbrush was allowed home with me after I cleaned it of hair and mobile, iPad, books and magazines went home with me.
Take plenty of drinks as copious amounts of fluids and urination help to clear the radioactivity. Take some hard sour sweets to stimulate saliva in case of dry mouth. Shower frequently every day (hospital towels supplied) as that also clears it.
I didn't have any side effects but nausea and dry mouth are fairly common. Nuclear physicist attended every day to monitor radioactivity. On the last day a full body gamma-ray scan was done to check uptake. It took around 40 minutes, isn't claustrophobic as your head is never entirely enclosed in the machine, a conveyor belt moves you under it and away again.
After discharge there are 21 days limitations on travel and contact, particularly with pregnant women and <18s. You'll be given a printed sheet detailing limitations. You can resume Levothyroxine as soon as you return home but it will take up to six weeks to rebuild levels. You may experience hairloss and very dry skin in addition to fatigue and other hypo symptoms. It will be due to low thyroid levels, not RAI.
I believe the level of uptake will determine whether further RAI is required. I had a low dose five months later which didn't require quarantine although the 21 day limitations had to be observed.
A few months after RAI thyroglobulin and thyroglobulin antibody blood tests will be done to measure thyroid activity. Mine have been <1.0 and <20 respectively for 3 years denoting lack of thyroid/antibody activity. They are now tested annually. They're treated as cancer markers as rising levels indicate there is thyroid activity which may mean there is recurrence.