Well.

[Greggy]

I often catch myself saying something mid-sentence, and when I do I just stop and I can't remember what I was saying, or if I was even saying any real words.

I don't know if I'm talking to someone, or just saying random words or just mumbling nonsense. No one has ever witnessed cause I never do it when anyone is around.

Should I be concerned? I have no idea what it is...

[Sith Lord 13]

Sounds like your internal monologue went out loud for a min. Not a big deal. Might raise a few eyebrows if you do it in public, but when you're alone, there's no issue.

[YouKnowWho]

That kinda happens to me too.
But it's someone in my head who narrates my life but they make my mouth and hands move too in order to narrate my life. xD

You're lucky you don't haven't done it in public! It's embarrassing, and people have laughed at me before. :(