Off topic...but should this person be doing deco dives,or would I want to buddy with them. There are many things that increase your sensitivity to toxing such as medications etc,but if you are experiencing symptoms then this should be a warning that you got out alive this time,but maybe not the next.
I certainly would be cautious, but on the other hand for all I know she might have:
- had nausea or something like that a few times on deco,
- didn't know for sure it was CNS/O2 related,
- switch to 80% for deco to experiment,
- seemed better so she stuck with 80% and never had the issue again.
Of all the risky things in cave/deco diving, sticking with 80% because its working for her seems moderate to me.