Keep thinking you are not sick, mind over matter is quite important here. You are not sick, but your body has had a fairly serious malfunction. You will do the radiotherapy because you need another malfunction like a hole in the head. Whether you keep working or not is a personal matter - I went back to work a week after a mastectomy and worked through chemo, BUT I had no fatigue or nausea and work helped me keep up the 'not sick but needing treatment' approach. I also didn't have radiotherapy. Many find some time out very beneficial, if only to get your head around what has happened. Best wishes, it's a long haul but you can get through it!