Thanks
@NetProphet . My frustration in those situations isn't just because I lose the match, but because I know I had it won against players who are better than me, and I don't realize what they're changing in their game that's making the match so much harder for me. When they start to catch up to me, I get more nervous and start playing more hastily, losing the calmness I had at the start of the match.
That's why I wanted some advice.
People react differently to these situations. Some people rush and try to go for too much, and some people try less and wait for the opponent to make a mistake. This is all about regulating your arousal. In your case, at that point in time, you needed to reduce your arousal level.
But it's not a trick you can just pull, you need to train it and be prepared. It starts with practicing mindfulness, so that you can be aware of your thoughts and self-talk. You can then use various techniques to reign in your thoughts. You can then identify whether you need to increase or decrease arousal, and what type of self-talk can help you achieve this. The type of self-talk is vital - you don't want to psych yourself up and increase arousal when you need the opposite.
Basically you need to engage in learning, work and preparation before you can really fix the issue, so take a look at the book I mentioned earlier. It's not a quick fix, it thoroughly addresses the issues, prepares you and sets you on the path to improvement.
PS: I remember when I first started TT 15 or 20 years ago, we did a best-of-41 points thing every week. I was playing someone and was up about 20 to 12 or something like that. I ended up losing 21 - 20. That still sits firmly in my memory - one game out of thousands that I've played. I remember the thoughts, the worry, the anxiety, the disappointment. So I understand completely, how you feel.
I rarely ever choke like that now, thanks to the work I've put in to address my issues. Recently I was playing a social game, late at night, where I was tired and lost focus. Before you knew it, I was down 9 - 2. Luckily, I realised what was happening just in time - my mind was wandering and was not focused. In this case, my arousal level had decreased, so I needed to increase it. I made the conscious effort to regain my focus, hype myself up and take it more seriously - even though it was just a social game. I won that game 11 - 9. Some luck was also involved

But without mental training and awareness, luck wouldn't have been enough to save that game.