This happens to me a lot. I think it’s definitely a breathing thing. I have one side that has trouble getting air and I can definitely feel a difference when it is more open. I make better decisions, I don’t drop basic stuff (especially tiger knees) and I feel like I can plan 2 moves ahead of my opponent, even if they are “better” than me. I can also feel the blood rush to my head, which is a physical indication that I’m firing on all cylinders. Also, after I’m done, there is an adrenaline rush.
Literally, if I can’t get that side of my nose open to move air up to my brain, I’m screwed. So I have to make sure I have coffee, Sudafed, a breathing strip, ANYTHING to get the job done beforehand.
Watching Viscant do his breathing exercises between matches kinda reinforces this.
Edit: Also, I subconsciouosly notice the backgrounds more. With all the little details in Marvel backgrounds, I just know when I’m more in the zone, I’m noticing the details that I won’t usually pay much attention to otherwise.