[dereg]

I'll push back because, in my experience, this sensation arises in the still-very-tired aftermath of totally spending myself on a problem.

Solutions emerge in my head as I sleep, usually after a day of brute-forcing a problem so much that it spills over into my mind's eye during breaks, which spill over into my dreams, where glowing forms congeal into solutions.

I recently read some comments here about people having vivid dreams of playing Tetris. That's exactly how my dreams feel, but in mine, I see either code, foreign languages, or a spreadsheet. Extending your gym analogy, it's like hitting your PR the day after going all-out on volume training.