I take a calcium supplement that has magnesium with it. I was told you should take magnesium like this because it would help absorb the calcium. The symptoms of a magnesium overdose sound like they are similar to many other things that could be wrong.
That must be why the doctors always tell you to be sure and list all of the medication and supplements that you are taking. Many times we think it is not necessary to tell them about the supplements, but often they can have interactions with the medications, so it is important for them to know about everything you are taking.