My head is a great deal better today. I can think again! There's still a little 'thickness', and a bit of pain at the head/spine area, I'm feeling good. I've been looking at foods high in magnesium and realised I don't eat many of them.
In addition to my horse-pills, I'll be increasing my intake of Mg-rich foods. My breakfast of granola and natural yogurt can be enhanced by tossing in some roasted cashews and pumpkin seeds. Instead of a couple of clementines mid-afternoon, I'll have a banana. Salmon will be a more frequent item on the menu, as will spinach. These changes, along with supplements should hopefully start to rectify the problem.
This morning I learned one of the other symptoms of magnesium deficiency is high blood pressure. An increase in Mg may well help my BP to be A OK once more.