"People With Schizophrenia Really Do Hear Voices—Their Own - The brain is a master storyteller, designed to make sense of the chaos of our lives. It compensates for the presence of auditory hallucinations, caused by a defect in self-recognition, by writing a narrative to account for them."

https://slate.com/technology/2016/03/schizophrenia-and-subvocal-speech-why-people-with-schizophrenia-hear-the-voices-of-god-spies-and-supernatural-entities.html

I was very stressed out yesterday and hearing voices. During that time, I also felt like my lips were moving along with the voices. I often feel like I have no control over my mouth muscles when the voices are speaking to me. I went to my therapy site to vent and learned a new term, regarding schizophrenia, subvocalizing thoughts. I researched it a little bit today. Here is the dialogue that instigated my internet search below.:

Danielle: Do you ever feel like you don’t have control over your mouth and it is being moved against your will? I mouth what the voices are saying or mouth the words to the songs on the radio. I feel like it is noticeable to other people. Is there a term for that?

Friend: My voices can control my eyes. And they control my breathing. And yes, I too have my mouth moved by subvocalizing thoughts.

Subvocalizing thoughts doesn't really explain why I feel my lips are moving though. Someone else mentioned that they suffer from this too and it is just a symptom of schizophrenia.