Your first sentence is correct, that is exactly what happened. You have some good ideas there... one of my first thoughts when it happened was "was I poisoned?". You can sometimes get a bad air fill in the tank, but usually you can taste this and it would affect you more at depth than at the surface. So it seems very odd that I was fine the entire dive, then had problems just as I removed my regulator. That is why I tend to focus more on physical issues, but of course I have seen little progress from that.
I plan on doing some big diet changes once the holidays are over... gluten free, anti-candida type of diets (elimination ones for a while). Thanks for your input.