How do you know that any of this is real?

Your senses could be lying to you quite easily.
Time is an illusion, that much is certain.
Maybe deja vu is just us remembering that we've done all this before. Does that mean there's no free will, because it's already happened? Or maybe we came back to change things? Maybe it's a simulation of what's already happened? Someone is trying to work out how things went wrong. Maybe you're supposed to be doing that but you forgot. Maybe none of this even matters at all.
Things don't happen. Nothing feels real.