Amazing how neither the actual radiation treatment nor the chemo "feel" like anything. If it'd weren't for the all the trimmings ( for radiation+ mesh mask, hard lead table, weird noises from the machine; for chemo: IV drips, beeping pumps, two hours in a chair) you would not even know you are getting treatment,

the kicker is in the after effects. for me both the actual radiation and chemo were totally painless and that's for both times. and you will definitely bounce back although not right after the TX ends. Radiation is the gift that keeps on giving.
My advice is don't worry but get yourself a TSH blood test now before TX Turns out however there is controversy over what is the right TSH level with labs having a 5.5, a 4.5 even though endocrinologists who went to Medical school the 21st Century consider 3.0 as the highest acceptable level. Before TX, I had a TSH of 1.6 and after TX it shot up to 4.3.
But without a pre TX baseline, you will have trouble getting TX if you need it. Lots of people never have any thryoid damage and they really try and zap the radiation beams around it. But better safe than sorry
Charm