Can rumination affect your cognition that much?

I'm a chronic overthinker and ruminate pretty much constantly. I often second-guess myself, lose focus, and have difficulty sustaining effort on cognitively demanding tasks.

A few years ago I scored 131 on Mensa Norway. More recently I found CognitiveMetrics and took CORE and AGCT.

CORE: 118 FSIQ, 121 Culture Fair
AGCT: 134

My CORE profile was quite uneven. Matrix Reasoning was around the 98th percentile and Comprehension around the 95th, but I did considerably worse on some working-memory, arithmetic, verbal, and block-counting tasks. I'm also not a native English speaker, so I don't put much weight on vocabulary-heavy scores.

During CORE I noticed something that happens to me fairly often: once questions became effortful, I started losing concentration. I would overthink, second-guess answers, struggle to sustain effort, and sometimes run out of time before properly reasoning through harder items.

AGCT was interesting because it heavily involved several areas I had performed crappily on in CORE, particularly arithmetic, verbal questions, and block counting subtests, while also being extremely speeded.

I took AGCT drunk (lol), because alcohol seems to heavily reduce my rumination and second-guessing and doubt. I was curious whether reducing the mental interference would outweigh whatever cognitive impairment alcohol itself caused.

Subjectively, the difference was huge. Instead of repeatedly checking myself, I would solve something, commit to the answer, and move on. I still ran out of time with roughly 10 questions remaining and randomly guessed those, getting most of them wrong (obviously), but still scored 134.

I'm aware of practice effects and I'm not trying to infer an exact “true IQ” from two tests.

What I'm interested in is whether severe rumination and excessive self-monitoring can produce this large a within-person difference in timed cognitive performance, particularly when the main effect seems to be hesitation, shitty attention, and inability to sustain effort rather than difficulty understanding the problems themselves.

Has anyone seen research or clinical data on performance differences of this magnitude from anxiety/rumination or excessive self-monitoring?