So if you change what is true, and you believe something that isn't really truthful, it will change your reality.
Your reality changing is what we call hallucination. You believe something is true which isn't. You believe something is out there which isn't.
"I am upset because I see something that is not there" is one of the first workbook lessons.
You see something that is not there because you believe it is a part of your reality. You believe it's part of reality because you believe there is truth in it. You justify it, explain it, prove it, emphasize it, focus on it, magnify it, rationalize it, and create it, all to demonstrate it is the truth - and you will then experience it.
When you "make" up the truth, you make illusions. You will experience those illusions as if they are real. And you'll think this is reality.
So because your perception, your mind, has to experience a reality that exactly matches what is true for you, if your belief about what's true changes from God's truth and turns false things into a truth substitute, then your mind is going to have to hallucinate in order to match that belief.
When you're experiencing your so-called reality, if it is not completely God's reality, you're still going to think it's real. You will take it for granted like it's just a given. Without questioning your truth you will just stay right there in your private hallucinated world.
The only way you can shift "reality" back to God's reality, is to change the truth. You need to look at, discover, realize and recognize what is true and what is false. Like, the real truth, not just something you want to be true.
This "sorting out" is a big part of the awakening process. What is true, what is false. And to transition from false to truth you're going to have to have "a little willingness" that maybe your "reality" is actually not showing you the whole truth - that you're seeing things that are not there - and that this is upsetting to you.
It's totally understandable that you would be upset by seeing something that doesn't exist. Scary as hell. To return to peace you need to stop hallucinating, which means you need to get really straight about what the truth really is. You can't keep playing ego games. You need to get super honest and discerning and find out, with Holy Spirit's light, what's really going on here.