The problem with standard magnesium blood tests (which are cheap, and therefore beloved by the nhs), is that they test blood levels, not cell/bone levels of magnesium. You need a biopsy style test to find out what is happening in the cells.
Magnesium in the blood can be fine, while the rest of the body is suffering deficiency, because the body maintains blood levels of Magnesium in order to be able to send it to the most needed location.
I heartily recommend this article for a clear explanation of why blood Magnesium tests only show severe deficiency, rather than less severe.
https://www.healthline.com/health/hypomagnesemia
In my own case, I had Magnesium deficiency, with several accompanying symptoms, a blood test did NOT show deficiency.
I was unable to absorb Magnesium supplements in tablet form, but responded superbly to Magnesium Oil rubbed into my skin. All symptoms of deficiency cleared up and continue to be clear, so long as I maintain the use of Magnesium Oil.
in answer to your question
@Cocosilk
Yes, I was deficient (like the majority of the population), but am no longer - with significant long term benefits to overall health, esp heart, blood glucose regulation and sleep quality. For which I am deeply grateful.