Obviously he has had his blood pressure checked at doctors appointments and stuff, but has he had it checked after standing for a few minutes? I developed orthostatic hypotension after my treatments ended - my blood pressure dropped when I stood up causing me to be light headed and all that. My pulse also races when my blood pressure drops. I had a tilt table test to confirm all of this. My blood pressure was going from 120/80 to 70ish/52 and my heart rate was getting up to around 135 when I stood up. My endocrinologist says it could be related to my neck dissection but my ENT says in the 20 years she's been doing the procedure she's never had it happen, not to say it is impossible or anything. It also could be related to chemo but no one has seen it happen from the chemo I was on. So basically they aren't really sure what caused it. But anyway, it might be worth looking into. But in any case, talk to your doctors about it.