my brain

Today I talked with Takeshi for about one hour. He is a Japanese man, 39 years old, and he have three children. We talked about children, Japanese school system...etc. It's really interesting. But I spoke too much Japanese. After that, for about 30 minutes, I couldn't speak anything in English. I don't know why. I felt exactly that my brain changed from English to Japanese. I was very supprised.
In dinner time, I talked about that for my hostfather. He laughed, and said, "Your brain prefer Japanese to English. Japanese is more natural than English for your brain." I said, "I know." And then, he said, " Be careful too much Japanese!"