Help me understand relationship between Potassium and Sodium

I have been suffering from adrenal fatigue for long time now and I'm keep getting confused about relationship between Potassium and Sodium. I have done Hair mineral Analysis test done and my sodium, potassium and magnesium were low.

Sodium- 15. Ideal number is 25.
Potassium - 5 Ideal number is 10.
Magnesium - 4 Ideal number is 6.

When adrenals are weak Kidney holds more potassium and excrete more sodium. I have been told by my nutritional balance practioner that I should avoid eating high potassium foodd like banana, orange, grapefruit, etc. and should take supplement to raise potassium level. My question is what's wrong with eating foods containing high potassium level? How do i balance out between sodium and potassium? I believe low cortisol also has to do with kidney holding more potassium?
Please someone explain this situation to me.

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