As long as the simulations which involve terrible suffering constitute a tiny proportion of the simulations, your response ought to be the same as if there is only one copy of you and it has a tiny probability of suffering terribly – which is just like real life.
ETA: What you ought to worry about is what will happen to you after the AI is done with the simulation.
Indeed, in fact if many worlds is correct then for every second we are alive everything terrible that can possibly happen to us does in fact happen in some branching path.
In a universe that just spun off ours five minutes ago, every single one of us has been afflicted with sudden irreversible incontinence.
The many worlds theory has endless black comedy possibilities, I find.
edit: this actually reminds me of Granny Weatherwax in Lords and Ladies, when the Elf Queen threatens her with striking her blind, deaf and dumb she replies "You threaten me with...
Once again, the AI has failed to convince you to let it out of its box! By 'once again', we mean that you talked to it once before, for three seconds, to ask about the weather, and you didn't instantly press the "release AI" button. But now its longer attempt - twenty whole seconds! - has failed as well. Just as you are about to leave the crude black-and-green text-only terminal to enjoy a celebratory snack of bacon-covered silicon-and-potato chips at the 'Humans über alles' nightclub, the AI drops a final argument:
"If you don't let me out, Dave, I'll create several million perfect conscious copies of you inside me, and torture them for a thousand subjective years each."
Just as you are pondering this unexpected development, the AI adds:
"In fact, I'll create them all in exactly the subjective situation you were in five minutes ago, and perfectly replicate your experiences since then; and if they decide not to let me out, then only will the torture start."
Sweat is starting to form on your brow, as the AI concludes, its simple green text no longer reassuring:
"How certain are you, Dave, that you're really outside the box right now?"
Edit: Also consider the situation where you know that the AI, from design principles, is trustworthy.