Neurocardiongenic syndrome and carotid sinus

My 10yr old grandson has had two fainting spells about three weeks apart and been dizzy on and off for a couple of months after that. He has also had a drastic body temperature change. He was always in flannel PJ's and now can hardly stand anything on  and yet he is freezing cold sometimes. He is very pale most of the time and has no energy, seems very tired all the time. His Dr. diagnosed it as Neurocardiogenic syndrome and suggested lots of water and salt in his diet. He did see a pediatric cardiologist and they did an echo and chest xray and he felt that was fine. They did the blood pressure laying, sitting and standing and it drops drastically leading them to think the syncope.  The last month he has not been able to stand anything close to his neck, he wants no collars and stretches out any t-shirt he wears to get it away from his neck. He said he feels like he's choking and can't stand it against his neck. We have read about carotid sinus and wonder if that is part of it. We are concerned they are missing something and wonder if you could suggest any further testing. Do you think a heart monitor for a month and check BP daily would help to figure this out. Would appreciate any other suggestions. Thank you so much for you input. A worried grandma