Let's look at what happens when you lie down and go to sleep.
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This is when most PN pain and discomforts arise with more strength.

When you lie down, your blood flow the to lower legs and feet
slows down. Whatever you have in your bloodstream just doesn't get to the toes and feet because of this. So indeed, any magnesium you take, orally, may no longer get to this target.

Soaking in epsom salts before bed may open up the small blood vessels and provide the magnesium this way. If you can find some topical magnesium product where you live, using it then may help. This slowed circulation, is what causes alot of calf cramping too. Even in people who don't have PN!

Compression in the lower back can also be a culprit. So getting a good orthopedic doctor and having imaging studies there done can reveal if you have some spinal reason for this painful and dramatic problem.