Googling the symptoms, and looking them up on medical websites, universally led to a diagnosis of hypotension (low blood pressure), which is not generally considered medically serious (certainly not life-threatening) and is NEVER treated with surgery. No other condition came up to match all of these but only these symptoms - the heart conditions I found which matched the treatment all included other symptoms and often didn't include one or more of the canon symptoms Chiharu displayed.
Would anybody here know of a medical condition that does match both the symptoms and the treatment?
I know it would be very easy to handwave Chiharu's ongoing medical care (after all, clearly the original author did), but medical issues are already addressed in the main manga, Chiharu's illness is a major part of his and Sumire's story, and I do want to deal with how a village of tengu who maintain a culture straight out of the Meiji Era are going to handle a medically-delicate human.
Searched terms: low endurance, dizziness, fainting spells, shortness of breath, cardiovascular surgery.