hi Trac
I am 30 years young

and i have had more or less the same probs as your husband.
I collapsed several occassions was taken to hospital , my white blood cell count was extremely high, which was also accompanied by severe stomach pain and they just kept putting me on antibiotics, i have long term low blood pressure problems. Which started when i had the collapsing phases. I have found out that my blood pressure is low due to the lack of blood flow going through my small intestine.
The dizzyness and headaches will be caused by his low blood pressure. Apparently it is healthy to have low blood pressure, less risk of heart disease or heart attack. But at times it doesnt feel healthy
After alot of tests i have just been diagnosed with crohn's. which they missed on several occassions!!!
MAybe it could be worth insisting they carry on testing and ruling things out until you are both happy with the diagnosis