This seems to corroborate my feeling that aptitude with language is a very poor proxy for intelligence, although it's often used as one. My own experience is that I'm less struggling to find the right words and sounds more clever at the times when my brain is actually empty and I'm "not there", and at the contrary the more "self-aware" I am and the more I struggle to articulate my thoughts, as if my brain (or ego?) was stepping in the way and slowing me down by trying to supervise what I'm saying too closely, making me sounds dumb.