First Day of Radiation

I had my first radiation treatment today and I am already tired 3 hours later? Also I felt a little sick afterwards and feels some stabbing pains? I really wasn't expecting to feel anything until 2 weeks into treatment based on what others in this group say they have experienced. So I don't think it is in my head because I wasn't expecting anything. Also my doctor said it sets in later during the day (but right now it is lunch time) and it is just that you go to sleep and when you wake up you feel fine. I just feel like every step of the way I keep underestimating how it will impact me. Even for my lumpectomy I had to take two and a half weeks off, although quite a bit of tissue was removed. Anyone else experience this, am I crazy? For reference I did not require chemo so I haven't had to deal with those side effects on top of radiation. Also for reference I am 41, maybe because I am not as active/healthy as some, not not to an extreme extent? I also mostly eat healthy and am vegetarian. Please share what you experienced and maybe what to realistically expect.