Do you have a reference for your assertion that Mg lowers sodium levels significantly?
The Cutler detox groups are full of people who are taking generous amounts of magnesium several times per day. Many also take extra electrolytes.
I've never previously heard that Mg has a negative effect on adrenals. On the contrary, there are plenty of people with anxiety who are putting extra stress on their adrenals. Mg is often nice for people with anxiety, including a close friend.