In shooter games the average player character is a super soldier. With limitless energy, nerves of steel and no reaction to pain or injury. Which is fine, they're games. But it's interesting that when some limitation or "realistic" gameplay mechanic is developed, players often react very positively. DayZ, Tarkov, Ghosts of Tabor, all thrived by including elements that allow the player to willingly suspend disbelief that little bit more. It's a type of difficulty that the player can engage with. Personally I'm not a huge believer in the "misidentified emotion" theory in games. I think, probably, the average shooter player just wants an experience that has a bit of realism, they don't want a simulation of the real world.

Having said that, if the average person was thrust into a situation where they were being shot at, or were wounded and under fire, and so on, they would be having a hard time controlling their own reactions to these events. Even just their breathing would be quite hard to control. And for some people that, in itself, could spell danger. If you hyperventilate and the amount of carbon dioxide in your system goes right down, panic can set in. So the question is, would it be possible to gamify these sorts of conditions with the aim of doing two things;

1. Adding a level of realism; specifically to the "embodied avatar" side of the gameplay, in a way that helps the player to further suspend disbelief.
2. To help to create a character arc that will continue through the character's self mastery and eventual empowerment.

One of the reasons why I like this type of idea is that feels like it creates a more rounded experience for the player. It reminds me a little of acting, or a performance. Someone like Danial Day Lewis is an amazing actor because of the level of detail he puts into the research and preparation for a role. To the point where, when we're watching him on screen, so much of what he's doing is below the level of our conscious awareness, it just helps us to accept that he is who he is in the world of the movie. Similarly, in games what a player wants is flow, from the outset. If we can create that and then take that player from one point to another, in terms of character arc, we'll have created a very satisfying experience.

I see adding to the realism of the embodied avatar as a sort of priming technique, that could work as well as audio or any other type of suggestion that belongs to the world of the game. The breathing input should fit into this, to allow the player to own the player character's development and to take control of their reactions where it's necessary, or important. We aren't going to ask the player to take every breath for the player character. But, equally, we want a system that creates emergent gameplay, not something that's a scripted or overly mechanical.