Can confirm. Sleeping in a tent on the Serengeti whilst hyenas and lions prowl around the perimeter of the campground has a noticeable effect on one's sleep pattern and heart rate.

From my own experience, "only" deep and intense breathing for not more than 5 minutes can alter state of mind drastically.

Am I correct that you meant:

> [...] something as simple as deep and intense breathing for not more than 5 minutes can alter state of mind drastically.

?

Because it seems some people are voting as if you wrote "[...] the only thing that can [...].

yes, you are correct, sorry for the ambiguity and late reply.

"Probably" seems like a massive understatement.