That is not something you diagnose and I doubt it's very important at all, just a different way of thinking. Words are just a way to communicate ideas but having the complete context of your own mind you don't need them, you can just think of the ideas directly instead of translating to words.

I myself have an inner monologue like 80% of the time and the times that I don't thinking seems faster. The downside is being harder to translate into words if I need to explain the idea to others.