You know that the very common hiatal hernia can cause fatigue, breathlessness, anxiety, panic and cardiac problems including racing heart and hypertension. And you probably know Dr Steven Rochlitz's book, Hiatal Hernia Syndrome/Vagus Nerve Imbalance.
It includes illustrations for self-correction of the hernia, the vagus nerve, the diaphragm. But it also relates that for some people corrections don't last long, and advises people to look into 2 often related conditions: PFO [aka the hole in the heart] and porphyria.
In fact Dr Rochlitz's books reveal that in some people with porphyria, the vagus nerve starts to demyelinate.
There's also an excellent one hour lecture/interview there.