it's a nice post indeed plo ufo !
I do think that to achieve this state of mind you have to be quite confident in your game. I actually don't think anymore about breathing, I just do it because it comes naturally in the flow of the game.
Once you feel better about yourself, it's all about feeling the flow and playing according to it.
I like PloUfo's advice a lot. The focus is on making the best decision with all the information that you have available. Slowing down is important. And then actively talking to yourself inside your head rather than acting on impulse. Actually, you basically say all this yourself. So you know it, but you just need to do it. So the thing is, just be.
PLO UFO is correct. The game has to be what's on you mind. Part of this game is figuring what your opponents have, remember they are doing the same thing. Just make the move and go back later for review. The game will always b challenging but over time your issue will be easier to deal with if you keep working at it. I have had this issue and at times I still struggle, easiest way to call it is I was not tunned into the game fully. Just be aware and keep working on it, there is a lot of solid advice on here so give it some thought