You can most definitely get into trouble with breathing exercises.
Just consider for a second what hyperventilating looks like, or hypo-ventilating. That is one of the things many pranayama and other breathing exercises do.
Restricting &/or increasing oxygen to the body/brain for extended periods of time… what could go wrong?
Aleister Crowley somewhat famously gave himself asthma doing some fairly extreme pranayama, which led to him using heroin medicinally which led to him using heroin somewhat less medicinally for the duration of his life.
Yes, the guy was known for going big on most things he did. But it is worth throwing in the asterisk.
While we all practice breathing since birth I do believe that trying some advanced techniques could be dangerous. See https://zeta.blue/physiology for possible effects.
People have unique physiological, and mental limits. As a toy example we could imagine someone holding their breath until they pass out and fall.
>we could imagine someone holding their breath until they pass out and fall.
It is not easy to imagine this. Brain have protective mechanisms in place to prevent this. If someone is holding their breath for too long - they start experiencing an immense, primal fear which magnifies tenfold every second. It is close to impossible to consciously bear that fear and continue holding your breath – every other second requires years of practice. You will inhale, if you can. Your body simply wont let you fail or pass out.
While I don't doubt there's a way to breathe so wrong that it has negative effects, I'm sceptical.
But I wouldn't think twice about swimming alone, so maybe I live on the edge.