I think wisdom and experience are pretty good things -- not sure how that relates though.

Some people I have encountered struggle with my rationality because I often privilege general laws derived from decision theory and statistics over my own personal experience - like playing tit-for-tat when my gut is screaming defection rock, or participating in mutual fantasising about lottery wins but refusing to buy 'even one' lottery ticket. I have found that certain attitudes towards experience and age-wisdom can affect a person's ability to tag ideas with 'true in the real world' - that reason and logic can only achieve 'true but not actually applicable in the real world'. It was a possibility I thought I should check.

And "screaming Cthulhu horror" was just a cute phrase -- I don't literally believe in Lovecraft.

I assumed it was a reference to concepts like Roko's idea. As for regular extreme misery, yes, there is a case for rationality being negative. You would probably need some irrational beliefs (that you refuse to rationally examine) that prevent you from taking paths where rationality produces misery. You could probably get a half-decent picture of what paths these might be from questioning LessWrong about it, but that only reduces the chance - still a consideration.