Headaches During Dialysis
The pathophysiology of dialysis-related headaches has not been completely elucidated. However certain factors seem to be associated with it, like sudden alterations in blood pressure, low levels of blood magnesium, high calcium or magnesium in dialysate fluid, etc. In addition, acute yet transient alteration in serotonin levels, cerebral vasoconstriction, hypoxemia, or renin-angiotensin-aldosterone disturbances contribute to headaches. For example, patients on dialysis with hypertension who have a sudden drop in blood pressure can activate their renin-angiotensin system causing vasoconstriction in order to increase their blood pressure.

Source: https://www.renalfellow.org/2022/07/12/headaches-during-dialysis-a-brief-review/