I'm surprised to learn the third myth is even a myth. My thoughts and feelings change significantly when I switch from sitting to walking/running or move from a

I'm surprised to learn the third myth is even a myth. My thoughts and feelings change significantly when I switch from sitting to walking/running or move from an indoor room to sitting outside in the sun. When I go from being in shape to out of shape my brain feels much more lethargic. I could go on but the general point is that changes in my physical condition have a big impact on my mental processes and vice versa. I had thought these responses were normal and the body and brain are deeply linked to each other. Do most people not feel these same effects?