Many times, over the years, I might have a a simple dental cleaning, then a week or so later, the headaches start. (I've read there are some kind of tiny nerve fibers that can be triggered by dental work.) This has happened so much that others have noticed it. Another thing, maybe two weeks before, I get these horrible leg cramps in the night in both legs at the same time. They can't be ordinary muscle cramps because they hurt in BOTH legs at the same time. They last for twenty minutes and hurt a lot!