I've found this happen to me on slots, each time with a larger amount being won. I'm wondering if others have experienced similar.
It all starts with a big win, or even a series of quite big wins that add up to a large amount. It's an amount you're satisfied with, it might mean paying off all your debts and finally being free of the weight hanging over you. You know deep down it's as good as it's going to get and there's absolutely no reason to carry on. And yet...
In my case, because I'd self-excluded years ago, this was using unregulated sites which had things like withdrawl limits and long "processing" times, meaning that a big win could take weeks to get out and even an amount in the process of withdrawing would be easily cancellable. The temptation to go back and take a look is always there.
So the part of your brain that wants you to keep playing says, first of all, "just have a little play, you've won so much that a couple of hundred doesn't matter". Or it might say "you're almost at a nice round number, it'll be easy to get that little bit more to get there". And you might win, in which case those previous messages get even louder - "this is basically free money to play with now" or you lose, and it says "next time has to be a win then, let's try again".
And then suddenly you're on a run of losses, something that seemed impossible when you were on your way up. All the way down, the logical part of your brain is setting limits "don't let it go below this, it's ok if can walk away with that" which the other part of your brain smashes through as it tries to get back up to where you started, where you apparently easily reached before. So a £200 bonus buy becomes £400, becomes £800. Any win becomes more fuel for the idea that you can get back to where you started. Any loss makes you more desperate. The logical part of your brain is looking for a way to get out with something but the other part has fully taken over and does not want to stop. In the end, the only thing that stops you is when the balance finally reaches zero.
The first time this happens is heartbreaking, you grieve over the lost money you never had and wonder how on earth it happened. The second time is infuriating, you thought you had learned a lesson, you already knew this could happen and somehow it happened again. The third time is absolutely traumatising, when it happens again after all that went on before, you realise just how big the problem is and feel utterly helpless, mentally and physically beaten.
I feel terrible for anyone else this sort of thing has happened to, I feel it takes a long time to process and to come to a time when you don't always think about it.