Two options: this reality is really real, or it isn't.
If reality isn't real, you're probably not going to be able to prove it's not real any time soon, nor figure out the real nature of reality. You're stuck here, in this fake reality, and so the stuff you do here will have the consequences it would have as if it were real even if it isn't. If you cut off your hand, it hurts and you have no hand. If you jump off a building, you break your legs - it really hurts, and it's expensive, and the recovery time is long.
If reality is real, then... all the same stuff above applies. You've got consequences that you have to live with.
The best option, I think, is to not worry about certainty, live your life as if it were real, because the consequences for messing up suck either way, but allow yourself a tiny little corner of your brain to acknowledge, every now and then, the tiny probability that it's all fake.