>>716212414It's like if you'd let a person experience every single cell of your body doing it's thing at the same time, all of the micro and macro processes that take place. Could you imagine, being cognizant of every red blood cell in your transferring oxygen at the same time? How it would feel for your guts to filter out useful material from food?
One of our brains' most useful trait is the ability to forget. And our body graciously does not have receptors for every single aspect of our bodies. People with ADHD can have difficulty forming coherent thoughts and keeping priority in their heads. And that's just with the "limited" information we consciously think of.
Now consider what fully experiencing a body larger than our little solar system would do to a human brain. That's what the Visitor does to Sam due to their miscommunication.