It may be commonplace to note this - again, I'm way too ignorant to say for sure - but the example I provided is interesting to me as an instance of achieving flow by temporarily going up, not down, in stress. Don't take this as advice, folks! A similar thing happens with excruciating pain when I'm able to focus.

I'm inviting discussion about a sudden shift in mind state that may be what some call flow, the zone, even enlightenment, that can (can it?) be encouraged by extreme (limit-) experiences (no escape, fight or die; physical pain stays, overcome or suffer), if they can be lumped together, approached pragmatically in a similar way, and so forth.