I know this is an old post but hopefully other people read this.
Before taking mag sups, I came across possible mag OD symptoms and although it is VERY unlikely to OD from magnesium, it's always good to have an idea of what those symptoms look like..
but to me, OP seems like he might have showed symptoms of overdose... muscle weakness, confusion..., inability to exercise.
Just look up magnesium overdose symptoms online..
i couldn't post a link because I just made this account today to post this lol. :/