Wow, that's interesting. I don't have badly low bp, but i have very good bp (which always surprises docs I think who expect it to be awful because I'm heavy).
Is this low bp all the time? Or something where the bp drops down really scary low while the person is sleeping?
Dr. Guilleminault has written a lot of papers on people with upper airway resistance syndrome and low blood pressure. There are other studies that show mostly young, thin women with "orthostatic intolerance" who get dizzy or light-headed when they stand up too quickly. They also tend to have cold hands or feet, and various nasal/sinus/headache issues. Interestingly, what I find is that as they age and slowly gain weight, the low BP becomes normal, and the cold hands get better, but later as they gain more weight (or after menopause in women), they'll have high blood pressure. Many young thin people with low blood pressure have at least one parent that have high blood pressure. I don't remember the exact mechanism, but I vaguely remember that it has to do with autonomic dysfunction. My wife has this too.