For an easy start have a look here:
If you want to dive deeper into the science here you go:
What doesn’t Kill Us by Scott Carney – Scott Carney explores the Wim Hof Method and some of the tremendous applications or breathing
Accessing the Healing Power of the Vagus Nerve – The best overview of how the nervous system functions.
These articles point to scientific studies of which I’d suggest you at least read the “abstract” or “conclusion”.
With all this: HAVE FUN! Use these sources as a joyful exploration of the amazing abundance of information that’s out there…not to find out how little you know and go into insecure scarcity mode!
Let me know if there are any questions.