Before Arnold became the governor of California in a "total recall" election he stared in an under-appreciated movie Total Recall.
Being an Arnold movie, it had a healthy dose of gratuitous violence. Being based on a Phillip K. Dick story it also included some angst about reality thrown in. The basic idea is that we meet Arnold's character in a futuristic world. He really wants to go to Mars, but he's a construction worker and can't afford it. He hears about "simulated vacations" and orders one where he goes to Mars as a secret agent. They put him under and next thing we see he wakes up, we're told the memory implantation failed, yethe does goes on a wild sci-fi shoot out just like the dream he ordered.
So was the vast majority of the movie us watching his implanted memories or watching his real life? I'm ambivalent about it and I think there is evidence on both sides, though I'm inclined to say it's real. As far as I know Arnold and the director haven't stated their beliefs (contra Blade Runner, is Harrison Ford an android?).
Most people think that this idea about doubting the existence of the external world is "deep" and "mind blowing." (What blows my mind is that people are willing to admit an Arnold Schwarzenegger action movie confused them.) But skepticism is a pretty banal old idea. Indeed, you've probably heard people ask, at least a dozen times, "if a tree falls in the woods and no one is there to hear it, does it make a sound?" You've probably asked yourself how you know other people are real and how you know you that they experience "green" when they see grass the same way you do. You probably concluded that you don't and never can know with certainly that other people exist or whether the tree would make a sound. The solipsist and other radical skeptic positions are irrefutable, though uninteresting. So if Total Recall is all a dream then anything can happen. There's no way to "prove" it's real because anything that is consistent with it being real is also consistent with it being a dream. Indeed, if you were a contrarian you could argue, without contradicting anything in the story, that The Lord of the Rings is all just Aragorn's dream and that Star Wars is just R2D2's dream (droids don't expect to be the hero, they just want 15 minutes of fame). But no one thinks that claims are remotely interesting or "mind blowing" do they?