Bear in mind that the "version of me" is me, and cognitively is in agreement that this is fine. Instinctively I would very much not think it was fine while undergoing the pain, but I'd also think I was wrong about that at the same time. I don't suppose I'd be all stoic about it like Giles Corey*, but it's the cognitive side of me that has the valid opinion and eventually the executive function.
*Squashed to death in Salem, 1692
Yea, this is where the argument has the biggest problems. If your heart explodes or you tear vessels in your eyeballs, or you have long term stress related tissue damage the fact you don't remember at all doesn't matter much.
The problem with memory is it exists in a lot of different places. Screw around too much and you can mess up organs or even your gene expressions. Nothing to do with your brain at all.
Scary stuff.
What's the practical difference other than timelike distance between you rather than spacelike distance?
https://oyc.yale.edu/philosophy/phil-176/lecture-12
Version 1: A mad scientist swaps your mind with another person's (Linda's), then asks which resulting body he should torture. Intuition says spare the one with your personality, so personality looks like the key to identity.
Version 2: He's going to torture you, but first gives you amnesia, then makes you believe you're Linda, then gives Linda your memories. Intuition says don't torture your body, so the body looks like the key.
Leaving that aside, is this really a great and clever question? In version 2, your minds are swapped, so it's the same question. The difference is that you have been "driven crazy" and "deluded", but in what sense? If the objective is to avoid yourself being tortured, it's unclear which one is yourself, simply because the question relies on the unclear fictional process of "making you believe you're the other person", and the question itself implies you shouldn't trust that process.
It could be made shorter: "A mad scientist comes along and does something mysterious, so that you might not be yourself any more! So, are you? Ah, you don't know! Gotcha!"
The original is in Problems of the Self, 1973. (Or it's an essay titled The Self and The Future.) I've got hold of that, am reading. The original version is really long. The first six pages are just really making a meal out of describing all the ramifications of the simple sci-fi concept of a body swap.
Yes, unfortunately it seems to be not very good. "He now further adds that at the moment of torture I shall not only not remember the things I am now in a position to remember, but will have a different set of impressions of my past, quite different from the memories I now have. I do not think that this would cheer me up, either." So, the problem with this is that it's nonsense, like saying "You are not you, but you are! Now if something happens to that person, does it happen to you?" Well I don't know, Bernard, it depends what your rather silly words mean. He's just playing the shell game with the word I.
Then at the end (ten pages later) there's a messier version: "he could have gone on and produced two persons each with A-like character and memories, as well as one or two with B-like characteristics". So it seems that the confusion and non-neatness of the swap is the whole point. Thing is, I'm not even very concerned which one is me. I suppose, alright, I do prefer me-like characteristics. So I'll take the half-dozen clones who seem vaguely right, that's good enough for me. Whatever.
It's enough that your nervous system adapts to the unsafe environment. It doesn't have to know why.
I mean, OK, there's plenty of further tricky sci-fi dilemmas along these lines. But I was interested in pain in the context of animal rights, obviously, this being a thread about whales.
I had a very gruesome femur break decades ago. I can remember begging to be knocked out because of the pain but there's no memory of the pain itself.