First of all, I'm not a pool instructor, so I hope it's okay to jump in here. I am a psychotherapist/psychophysiologist as well as the lifelong pool enthusiast. I have been studying and applying applied psychophysiology since I was first introduced to it in 1977. In my practice, I work with ADHD, optimal performance, and other issues in which focus, or more specifically the type of focus, or the ability to have variability in the type of focus is the key to optimal success. I lurked, and then joined Azbilliards.com because along the way of educating myself, I've had the opportunity to train with some psychologists who work with Olympic and other high-level athletes for optimal performance. While in this training my focus often goes to "these concepts are probably more applicable to pool than most of the sports that they're being used on" I'm at the stage of refining/researching what I want to say and the best venue to do that in. I started off trolling the main forum and then found my way over to this forum with the hope of sharing my experience without too much crap from the peanut gallery.....
There's a psychophysiological reason for the 20 minutes you describe. It's called secondary shift. The autonomic nervous system regulates and runs the body based on our interpretation of our environment real or imagined. Another concept is homeostasis or that the body has a thermostat of sorts that keeps you between the "yellow lines" of where you tend to function particularly over the last six months or so. If I were monitoring someones physiology with biofeedback or neuro- feedback and they were doing meditation or something that takes them outside their yellow lines; after about 20 minutes the nervous system without cognitive influence would tend to elicit arousal, or in pool language take you out of dead stroke. It's important to remember that all of this is plastic. It can change over time for the better or worse. There is no doubt that by applying specific techniques and particularly enhancing that with immediate feedback of what you're trying to achieve learning can and does take place.
I believe in pool, to optimally perform we have to be able to shift states frequently and be good at it. I know for myself when I'm patterning. deciding where I want to hit the cue ball, checking my set up and visualizing the outcome; that state is different from my optimal "stroke" state.
Breathing was mentioned earlier in the thread, and in another post I would like to talk in more detail about optimal breathing. When we look at respiration and the autonomic nervous system, breathing is particularly useful because it is unique in that it is the only part of the autonomic nervous system that is under voluntary control when we are conscious. This has what we call an afferent/efferent effect on the nervous system. That means that information comes from the brain,
to the body but we can also feed information into the nervous system
from the body. If you'd like to know more about breathing and optimal performance you might want to check out this YouTube video explaining it in more detail by one of the original researchers.
https://www.youtube.com/watch?v=9nwFUKuJSE0