You can be certain of something and change your mind later when presented with new evidence. Sometimes it's best to just commit. Especially in this case where you're already living your life under the assumption that you can tell the difference between reality and a fever dream.

But maybe you are weird and question yourself frequently if you're experiencing reality or not, and if that's the case that just seems unhealthy to me.

Either way, I'll continue to be certain that my reality is real until there's evidence to the contrary.