It doesn't really make any sense how this could possibly be related, and for that reason I don't rule out some other factor being at play, but the correlation has been pretty evident on all 3 occasions when I tried to do this and the absence of the same effects when I don't do this and instead do pre-boil the pasta all seem to point it being the relevant variable.
Assuming the no-pre-boiling somehow is responsible, the obvious solution to the problem is to just stop doing that and indeed I have for fear of a repeat of the horrible experience, but it's just that the ease and efficiency of the method is so appealing and I would like to try it again, but I also really don't want to gamble on that unless I can be pretty well assured that the results were unrelated to the lack of a pre-boil or if that actually is a plausible cause, I'd like to learn by what mechanism this could possibly play a role and why it doesn't bother most people.
Boiling the pasta removes some of the starches from the pasta, which is why people recommend adding some pasta water into your sauce. Maybe you're allergic to those starches?
Or, maybe it was an overload you weren't used to. Definetly think the starch is the issue.