Checking back, a year later, as I see some people know exactly the feeling I'm talking about.
I have however found nothing conclusive, only speculations. Some think it's like a voluntary release of adrenaline, or manipulating the nervous system etc. I found one post that claimed to have ran some tests aswell:
"I have been practicing western medicine for 30 years and for a change also just completed my masters in Oriental Medicine (2014). [We] have for years used different equipment to play with my "ability" while in the ER/OR/Office while no patients: PulseOX, EEG, EKG, spirometry.Th