My husband went thru phases of extreme headaches, even ER-level headaches. The worst was when the pain started to cause throwing up, which shoots up the blood pressure, and it becomes an endless cycle.
Sometimes we didn't know the cause, but I think dehydration was the culprit a lot of the time. Are you getting too dry?
If you don't think you're dehydrated, remember that even if you still have fluid in your tissues, you can be dehydrated in your blood. After dialysis takes most of the fluid out of your blood, it can take a bit of time for the tissues to pour more excess water into the blood, so you can go through a period of extreme dehydration if you just keep pulling fluid. When we did home dialysis, sometimes we'd set the machine to take off zero for a half hour or so while the body catches up to it, or even add saline. In-center, he'd usually try to drink water or ask for some extra saline, even if he hadn't reached his goal and was continuing to dialyze..
I will encourage you, though, that he seemed to "get over" the headache phase after a while and not have them for several months at a time. He was like that with all his symptoms. Docs thought it was just the body's cycles.
I feel for you, I've seen the pain of dialysis headaches