wait can everyone consciously do this? i can't
But if you try to do it, you will concentrate on each nostril in turn and little else, in synchronisation with your breathing, which leads to the kind of mild auto-hypnosis that the GP is talking about.
http://mentalfloss.com/article/30363/why-does-your-nose-get-...
" Throughout the day, they each take breaks in a process of alternating congestion and decongestion called the nasal cycle. At a given moment, if you're breathing through your nose, the lion’s share of the air is going in and out of one nostril, with a much smaller amount passing through the other. Every few hours, your autonomic nervous system, which takes care of your heart rate, digestion and other things you don’t consciously control, switches things up and your other nostril does all the heavy lifting for a little while. The opening and closing of the two passages is done by swelling and deflating erectile tissue - the same stuff that’s at work when your reproductive organs are aroused - up in your nose."
Given that pretty much everything in the human body is linked to the nervous system in some manner, it's possible that there might not be a good reason to expect any kind of special feedback loop here.
Try to breath in through one nose hole and breath out through the other. This may sound stupid, but there are two reasons why this works:
1. You focus on doing something else than thinking about stuff that worries you. 2. While doing this your eyes move from left to right. You might remember what hypnotists do: They swing a pendulum from left to right which you have to follow. This eye movement from left to right activates your subconscious part of the brain. I don't know or remember what exactly that does but everytime I use this technique and wake up the next morning I don't remember doing anything after this. Which means I fell asleep.