My magnesium is normal on bloodwork, why do I feel depleted?

Because serum magnesium, the version measured on standard bloodwork, represents less than 1% of the magnesium actually stored in your body, mostly in bone and muscle. A widely cited ICU study found normal serum magnesium in the majority of critically ill patients who, on direct muscle tissue testing, actually had significant magnesium depletion; the two numbers barely correlated in the same people. Blood is tightly regulated because the heart depends on it staying stable, which is exactly why it's a poor proxy for what's stored in tissue. A tissue-level reading, like an OligoScan, is looking at a different compartment entirely, one that a standard blood panel isn't designed to capture.