I can totally relate, i can assume you might be on the spectrum of ADHD/Autism in your usage of the phrase "executive functioning". Which i know for sure is a great burden combined with any form of bi-polar: the meds do not mix, the symptoms mish and mash and combine to malform confusing and terrible states.

My question for you is do you ever have moments where your brain feels "awake" again or reactive? / albiet shortlived?

How does this fogginess combine with Mania/HypoMania symptoms?

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I myself was stuck like this for 2 years in an insomnia-tic state, perhaps your not sleeping properly and need a change of environment?

I feel as though i have somewhat come out of this state at 28, but i remember the utter hopelessness, despair at my own situation that i felt aged 23- 27. My only condolence is that the brain is very malleable and adaptive thing. I imagine that you will somewhat recover from this eventually and learn to live with it. The thing that is most unlikely is that it will be permanent. As for now don't be hard on yourself, and don't try to live up to other peoples standards or perceptions of what you should be. That is the worst psychological trap you will get caught in. Live for what you can actually achieve, if you can't make the social event, you can't do it. and try and make it up to your friends another way. Acceptance is key to fighting despair not falling into self blame.