I was tired even before radiation started, due to chemo, which was far worse than radiation was. Everyone is different. About 10 -14 days or two weeks, most start feeling the radiation effects, the worst being the last two weeks up to two, three weeks post treatment, as mentioned. Chemo effects start just afer a few days of infusions, and can be simlilar to radiation side effects with Dry mouth, mucocitis, thrush, etc and compoud the radiation effects, but are mostly acute, and side effects not as long lasting as radaition effects. Good luck.