Not sure of the question, is this common with chemo? I assume you are speaking about adverse side effects making treatment impossible? I say yes, maybe not to mine or your extent, but you will see more patients that are unable to complete chemo treatments as opposed to radiation due to adverse side effects, labs, and is often underestimated, I know I did. My cancer did spread/return due to not having curable treatment (radiation) in a timely manner, plus the inability to have chemo with radiation up to three years later, and limited to a few types, and low dosages only. My original ENT said if I did not have such a reaction I probably would have been cured by now. That was 4 years ago.
As far as what you can do? The best you can. That's all. What may not be appropriate today, may be tomorrow. If you did 4 weeks radiation, had a clear PET, you did well, especially after your horrific encounter. The main thing is we are here. My doctor once told me it doesn't matter what adverse affects you had, what matters is you were strong enough to pull through and survive.
Be well.