Hi Tim,
Congrats on finishing FSR...28 sessions is a long time. I know I felt a sense of accomplishment after my one treatment (even though the docs did all the work), so it must feel good for you to be through with it.
I didn't experience the head-fullness like you are, but I'm quite familiar with the side to side thing. On a bad day just looking over my shoulder can set off waves of wobbliness. My doc calls it oscilliopsia. Had it before getting zapped too. Vestibular therapy is helping, especially gaze stabilization exercises, which can be done standing or sitting. After about 2 months of 2x per day exercises, the unsteadiness has diminished by maybe half.
I do hope the fullness and dizziness you're experiencing is a short term after-effect of the radiation. Let us know what your doc says.
Best wishes to you,
Betsy