Hi Jesse - my sister had this procedure done to kill her thryoid for Graves Disease. She did not have to have it removed, just irradiated. She is fine and healthy now but it was a little difficult. At first when she was so incredibly grumpy and irritable because of overactive thyroid and then afterwards when she went super slow - It was a matter of finding the right dose of medication which can take a month or two at least. She needs tune-ups as well.
A friend had surgery done to remove her thyroid because they found cancer. This was about 6 yrs ago. They also did radiation. Her scar is not noticeable and has faded as time goes on. She just had a baby and doesn't complain of any problems from the thyroid issue.
Both my sister and friend said that the radiation treatments made them very tired. The worst was during treatment and then for a good month afterward. Just in the past few years there have been advances in techniques in delivering radiation to avoid damaging surrounding tissues. I can imagine you're going to be in great hands!
Best of all things to you - hope you're 100% very soon.
p.s. I am also 42 but I am a mom of 2 boys - ages 6 and 2. Now that I'm getting to be "my age" I'm kind of understanding why God intended us to have kids in our youth! I'm loving every minute - no complaints on my end. - C