Not exactly mutterings.
Full sentences commenting on something or other, but realizing, that there is no one there to hear what you just said.
Except yourself, which, I suppose, must be good enough.
Have you experienced this? Would you admit to it, if you do? I find myself not exactly having full blown conversations with myself, simply a comment or two, usually about something I am observing.
"Why is she/he wearing THAT?" I'll ask aloud. Perhaps, if I am in earshot of someone, they will think I am talking to them and answer. I'll smile, respond to their comment, and know perfectly well that I hadn't asked them for their opinion. Perhaps, they too, are commenting to themselves on what they were observing and it was simply coincidental that I was near enough, as well, to hear their thoughts.
In any event, I used to be somewhat chagrined at my own behavior. Is this the precursor to something infinitely more serious? Should I discuss it with a professional? Did I just ask myself that very question, aloud? Did I respond?
Not to worry.
I suspect when the time comes and I am not aware of my aloud utterances, friends and family might join together to look into this, and do something proactive.
For now, it is comforting to know that I have an enraptured audience. Me.