Everyone gets some form of that. For me, when reading alone I am 99% fluent. Worst is talking to my family, often the easiest to talk is with strangers and it's exactly in those moments when I am meeting someone completely new that I get those awesome moments of complete fluency. It's weird and I can't explain it especially since I don't mind stuttering around my family and feel anxious about it when near strangers so logically it would have to go other way around.