I'm sorry to hear your husband has been going through this. I know this is trying for both him and you. I had no idea there was any problem until I had a headache from a BP in crisis stage. It took a year and a lot of money to get to the bottom of this for me. They put me on BP meds and a water pill, which have their own side effects that turned my life upside down. I've experienced syncope, blurred vision, and an awful feeling when my BP drops out. I've done several face plants from weakness and blacked out once. I'm going in for a heart ECHO to see if my ascending aorta has dilatated further. Occasionally I get headaches when it spikes. I've dropped some supplements, changed my diet, and exercise more. I monitor my BP multiple times a day and medicate accordingly. Currently, I'm on 10mg Losartan, and fluctuate between 12.5mg and 25mg of hydrochlorothiazide. This has greatly reduced the number of incidents during the day. Nighttime is another issue. Currently, I am experimenting with my sleep position as I find when my feet and heart at the same level, I experience hypertension. I have Hydralazine on hand when it goes into crisis stage. All of this is time consuming and annoying, but better than staring up at dandelion roots. I'm not saying this regime will work for everyone, but it is helping me, at least to feel like I have some control. It appears most doctors are unaware of the side effects of head and neck cancer treatment, but I've read studies drawing attention to the problem, so awareness may grow. I posted here just to bring it to attention of those who are looking for answers. Hopefully, your husband will find his.