In the previous post we looked at one sort of mental malfunction, and as I went through the comments (much appreciated, and empathized with!) I recalled a horror story of my own from earlier this year. In the second round of a club tournament the position in a queenless middlegame was pretty complicated, and my decision was also a two-mover of sorts. To decide on my 24th move I had to weigh a pair of options on move 25, and after spending eight of my last 22 minutes picking a 25th move option I was happy with made my 24th move and rushed off to the restroom for a final time before zeitnot.
When I came back to the board, my opponent had made the move I expected, and I immediately replied...only to realize with Kasparovian horror (but a slightly better poker face) that the move I played was the one I had rejected. Oof. Fortunately it wasn't much worse than the intended move, and the game turned out alright. Still, the feeling of horror was mind-blowing when I realized what I had done. It's not just the quality of the move and the sporting repercussions that come into play, but a feeling of helplessness - one thinks one thing and does another. As far as I can recall that's the only time that this sort of error has happened to me, whether as victim or recipient, but I have seen other examples of this sort in the literature.
Has that, or anything similar, happened to you?