Hi Gemma,
I'm surprised your Oncologist said that. I was told flat out it was going to suck! But then it also depends on your definition of sickness. Initially, say for the first week or two, you won't feel much, but as time goes on, it gets pretty rough. Throat pain, swallowing issues, sunburn like symptoms on your neck, fatigue etc. Side effects vary and are different for each person but it's pretty safe to say that unfortunately, you'll be feeling pretty crappy as time goes on. Start now if you can with a lotion for your neck. Use it several times a day (but NOT before a treatment!) to help prepare your skin for the rads. I used "Special Care Cream" but there are several that will do the trick...ask your team.
I had chemo too but other than added fatigue and nausea I did Ok with it.
Good luck with everything. This is a great place for info and support as you go through treatment.
Positive thoughts and prayers
"T"