But isn't this extremely exhausting and time-consuming? And if it indeed works this way, then where do you think the idea you are trying to formulate in your inner monologue comes from?
There are some things that are explicitly visualized, like an object I'm thinking about, where I wouldn't say in my head "I am imagining the sun. It is bright. Etc. etc.". I'd just picture the sun, and my "narrative" would probably be about why I was thinking about the sun, not describing it.
Same applies for more abstract concepts, just without the visualization.
Perhaps experiments using techniques such as PET scans might reveal if there is something more characteristically linguistic going on in those of us who feel we have an internal monologue.