My husband was getting syncope, but he is also diabetic. We have an oximeter and we also take his blood glucose readings and check his blood pressure. He was having "white outs." Breathing and oxygen is at better levels when lying down, rather than sitting. We do the 15 minute watch for low glucose: a few ounces of classic coke, a small snack and test again in 15 minutes. Usually resolves. We have glucose tabs everywhere, including in the car. It took a couple of years to sort this out. We went to a pulmonologist.