I’m convinced this is a special case of the more general “success begets success”. There’s likely a physical aspect of it as well but just feeling like you’re doing well drives you do better. It’s a virtuous cycle.
This is something well proven, that over certain temperature, mathematical work drops enormously.
Having experienced that I have the hypothesis that the body regulates the temperature of the brain and if it is too high it will make it to slow down, just like a computer does and make you lazy so you do not generate more heat.
In the same way, it makes sense that if your lymphatic circulation is blocked, as it works only with movement, it will make you lazy so your cells do not generate more waste that can not be cleaned.