What does triggering your gag reflex do for your HRV scores?? I am genuinely curious, and I think this technique is under-rated as a way to stimulate your vagus nerve.
Go on, stick that hand down your throat. No shame.
fake it till you make it
We already have good data on cold water in general. http://www.ncbi.nlm.nih.gov/pubmed/21941017
Interesting about eyes being open, though. Why do you say that? Intuitively, it makes sense somehow. The whole face is very "vagal". I get an increase when I intensely stare at something, as if I was hunting.
just for giggles, try measuring during a good poop. inverted seismograph.