Okay so you're in the grip of unknown unknows. You don't know you're wrong because you're not sufficiently familiar with the material. Private meditation is not sufficient for understanding or discussing language, perception, cognition, or really anything. You're not "making things up". There are a variety of models but one that I favor suggests that your brain is made up of many non-conscious modules or agents that interact to produce higher level speech, utterances, behaviors, whatever. Your conscious self doesn't know what's going on down there but those modules are thinking and engaging in complex decision making. The same way that a person may have never heard of calculus but can perfectly map the trajectory of a thrown object in 3d space without being consciously aware of how they're doing it.

They're handling the grammar, the vocabulary, cross referencing information in your memories, evaluating what is and isn't significant, and applying other processes that you don't need to be consciously aware of. You're probably aware from your meditative practice that things go a lot smoother when you're not acting consciously. You're confusing a lack of consciousness for a lack of complexity. The non-conscious parts of your brain, the parts that handle the majority of our cognitive functions, are very smart. They just don't report things to your conscious self unless high-level executive function is needed.

Also, definitions; the unitary self is illusory. Sentience, the ability to feel and perceive, is not. It's a very important distinction.